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 $144.70   8.622%   $157.176   $157.18   $157.20   $157.20  
  Purchase #2 $193.36   3.846%   $200.7966   $200.80   $200.80   $200.80  
  Purchase #3 $12.44   6.601%   $13.2612   $13.26   $13.25   $13.30  
  Purchase #4 $38.66   7.221%   $41.4516   $41.45   $41.45   $41.50  
  Purchase #5 $153.92   10.410%   $169.9431   $169.94   $169.95   $169.90  
  Purchase #6 $125.26   11.406%   $139.5472   $139.55   $139.55   $139.50  
  Purchase #7 $236.32   4.151%   $246.1296   $246.13   $246.15   $246.10  
  7 purchase totals = $904.66       $968.3053   $968.31   $968.35   $968.30