Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $247.53   11.668%   $276.4118   $276.41   $276.40   $276.40  
  Purchase #2 $99.78   4.348%   $104.1184   $104.12   $104.10   $104.10  
  Purchase #3 $240.36   6.226%   $255.3248   $255.32   $255.30   $255.30  
  Purchase #4 $113.53   7.465%   $122.005   $122.01   $122.00   $122.00  
  Purchase #5 $214.76   11.603%   $239.6786   $239.68   $239.70   $239.70  
  Purchase #6 $226.88   11.333%   $252.5923   $252.59   $252.60   $252.60  
  Purchase #7 $220.43   9.392%   $241.1328   $241.13   $241.15   $241.10  
  7 purchase totals = $1,363.27       $1,491.2637   $1,491.26   $1,491.25   $1,491.20