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 $37.63   10.674%   $41.6466   $41.65   $41.65   $41.60  
  Purchase #2 $161.30   5.671%   $170.4473   $170.45   $170.45   $170.40  
  Purchase #3 $204.48   4.244%   $213.1581   $213.16   $213.15   $213.20  
  Purchase #4 $248.52   5.699%   $262.6832   $262.68   $262.70   $262.70  
  Purchase #5 $38.95   3.767%   $40.4172   $40.42   $40.40   $40.40  
  Purchase #6 $213.72   10.281%   $235.6926   $235.69   $235.70   $235.70  
  Purchase #7 $30.29   11.497%   $33.7724   $33.77   $33.75   $33.80  
  7 purchase totals = $934.89       $997.8174   $997.82   $997.80   $997.80