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 $68.59   6.403%   $72.9818   $72.98   $73.00   $73.00  
  Purchase #2 $215.53   13.407%   $244.4261   $244.43   $244.45   $244.40  
  Purchase #3 $45.62   10.303%   $50.3202   $50.32   $50.30   $50.30  
  Purchase #4 $160.88   5.403%   $169.5723   $169.57   $169.55   $169.60  
  Purchase #5 $124.87   7.439%   $134.1591   $134.16   $134.15   $134.20  
  Purchase #6 $53.27   4.104%   $55.4562   $55.46   $55.45   $55.50  
  Purchase #7 $14.39   5.604%   $15.1964   $15.20   $15.20   $15.20  
  7 purchase totals = $683.15       $742.1121   $742.12   $742.10   $742.20