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 $38.83   6.740%   $41.4471   $41.45   $41.45   $41.40  
  Purchase #2 $229.35   12.652%   $258.3674   $258.37   $258.35   $258.40  
  Purchase #3 $206.65   3.695%   $214.2857   $214.29   $214.30   $214.30  
  Purchase #4 $107.33   11.638%   $119.8211   $119.82   $119.80   $119.80  
  Purchase #5 $164.43   5.576%   $173.5986   $173.60   $173.60   $173.60  
  Purchase #6 $216.40   4.532%   $226.2072   $226.21   $226.20   $226.20  
  Purchase #7 $157.36   4.761%   $164.8519   $164.85   $164.85   $164.90  
  7 purchase totals = $1,120.35       $1,198.5790   $1,198.59   $1,198.55   $1,198.60