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 $65.26   13.772%   $74.2476   $74.25   $74.25   $74.20  
  Purchase #2 $183.31   11.796%   $204.9332   $204.93   $204.95   $204.90  
  Purchase #3 $240.73   6.474%   $256.3149   $256.31   $256.30   $256.30  
  Purchase #4 $160.83   5.424%   $169.5534   $169.55   $169.55   $169.60  
  Purchase #5 $124.99   10.338%   $137.9115   $137.91   $137.90   $137.90  
  Purchase #6 $23.93   3.745%   $24.8262   $24.83   $24.85   $24.80  
  Purchase #7 $117.97   10.749%   $130.6506   $130.65   $130.65   $130.70  
  7 purchase totals = $917.02       $998.4374   $998.43   $998.45   $998.40