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 $179.87   8.203%   $194.6247   $194.62   $194.60   $194.60  
  Purchase #2 $236.47   6.302%   $251.3723   $251.37   $251.35   $251.40  
  Purchase #3 $227.66   3.145%   $234.8199   $234.82   $234.80   $234.80  
  Purchase #4 $29.78   13.460%   $33.7884   $33.79   $33.80   $33.80  
  Purchase #5 $59.54   11.394%   $66.324   $66.32   $66.30   $66.30  
  Purchase #6 $153.81   12.422%   $172.9163   $172.92   $172.90   $172.90  
  Purchase #7 $200.98   5.729%   $212.4941   $212.49   $212.50   $212.50  
  7 purchase totals = $1,088.11       $1,166.3397   $1,166.33   $1,166.25   $1,166.30