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 $108.44   8.593%   $117.7582   $117.76   $117.75   $117.80  
  Purchase #2 $122.53   6.465%   $130.4516   $130.45   $130.45   $130.50  
  Purchase #3 $199.43   12.283%   $223.926   $223.93   $223.95   $223.90  
  Purchase #4 $44.69   5.217%   $47.0215   $47.02   $47.00   $47.00  
  Purchase #5 $210.40   11.533%   $234.6654   $234.67   $234.65   $234.70  
  Purchase #6 $166.88   10.317%   $184.097   $184.10   $184.10   $184.10  
  Purchase #7 $164.53   9.658%   $180.4203   $180.42   $180.40   $180.40  
  7 purchase totals = $1,016.90       $1,118.3400   $1,118.35   $1,118.30   $1,118.40