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 $205.87   11.106%   $228.7339   $228.73   $228.75   $228.70  
  Purchase #2 $26.58   10.265%   $29.3084   $29.31   $29.30   $29.30  
  Purchase #3 $227.34   5.697%   $240.2916   $240.29   $240.30   $240.30  
  Purchase #4 $154.70   4.335%   $161.4062   $161.41   $161.40   $161.40  
  Purchase #5 $225.53   8.586%   $244.894   $244.89   $244.90   $244.90  
  Purchase #6 $102.46   7.379%   $110.0205   $110.02   $110.00   $110.00  
  Purchase #7 $10.52   13.781%   $11.9698   $11.97   $11.95   $12.00  
  7 purchase totals = $953.00       $1,026.6244   $1,026.62   $1,026.60   $1,026.60