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 $29.33   5.603%   $30.9734   $30.97   $30.95   $31.00  
  Purchase #2 $124.90   10.498%   $138.012   $138.01   $138.00   $138.00  
  Purchase #3 $140.88   9.516%   $154.2861   $154.29   $154.30   $154.30  
  Purchase #4 $102.72   4.729%   $107.5776   $107.58   $107.60   $107.60  
  Purchase #5 $231.75   5.355%   $244.1602   $244.16   $244.15   $244.20  
  Purchase #6 $191.97   9.591%   $210.3818   $210.38   $210.40   $210.40  
  Purchase #7 $22.79   11.538%   $25.4195   $25.42   $25.40   $25.40  
  7 purchase totals = $844.34       $910.8106   $910.81   $910.80   $910.90