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 $225.97   10.779%   $250.3273   $250.33   $250.35   $250.30  
  Purchase #2 $195.29   10.260%   $215.3268   $215.33   $215.35   $215.30  
  Purchase #3 $201.73   13.502%   $228.9676   $228.97   $228.95   $229.00  
  Purchase #4 $56.85   8.341%   $61.5919   $61.59   $61.60   $61.60  
  Purchase #5 $70.33   7.161%   $75.3663   $75.37   $75.35   $75.40  
  Purchase #6 $10.28   10.451%   $11.3544   $11.35   $11.35   $11.40  
  Purchase #7 $151.63   4.871%   $159.0159   $159.02   $159.00   $159.00  
  7 purchase totals = $912.08       $1,001.9502   $1,001.96   $1,001.95   $1,002.00