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 $10.61   12.629%   $11.9499   $11.95   $11.95   $11.90  
  Purchase #2 $83.63   12.139%   $93.7818   $93.78   $93.80   $93.80  
  Purchase #3 $98.25   11.425%   $109.4751   $109.48   $109.50   $109.50  
  Purchase #4 $213.83   6.303%   $227.3077   $227.31   $227.30   $227.30  
  Purchase #5 $23.29   11.312%   $25.9246   $25.92   $25.90   $25.90  
  Purchase #6 $216.68   4.170%   $225.7156   $225.72   $225.70   $225.70  
  Purchase #7 $88.97   13.282%   $100.787   $100.79   $100.80   $100.80  
  7 purchase totals = $735.26       $794.9417   $794.95   $794.95   $794.90