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 $180.49   11.368%   $201.0081   $201.01   $201.00   $201.00  
  Purchase #2 $125.94   12.608%   $141.8185   $141.82   $141.80   $141.80  
  Purchase #3 $241.63   4.437%   $252.3511   $252.35   $252.35   $252.40  
  Purchase #4 $18.49   12.438%   $20.7898   $20.79   $20.80   $20.80  
  Purchase #5 $106.66   3.544%   $110.44   $110.44   $110.45   $110.40  
  Purchase #6 $116.96   3.838%   $121.4489   $121.45   $121.45   $121.40  
  Purchase #7 $8.33   7.506%   $8.9552   $8.96   $8.95   $9.00  
  7 purchase totals = $798.50       $856.8116   $856.82   $856.80   $856.80