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 $221.53   10.118%   $243.9444   $243.94   $243.95   $243.90  
  Purchase #2 $44.42   3.283%   $45.8783   $45.88   $45.90   $45.90  
  Purchase #3 $151.27   5.848%   $160.1163   $160.12   $160.10   $160.10  
  Purchase #4 $58.64   7.328%   $62.9371   $62.94   $62.95   $62.90  
  Purchase #5 $149.80   9.473%   $163.9906   $163.99   $164.00   $164.00  
  Purchase #6 $184.50   11.507%   $205.7304   $205.73   $205.75   $205.70  
  Purchase #7 $41.84   8.670%   $45.4675   $45.47   $45.45   $45.50  
  7 purchase totals = $852.00       $928.0646   $928.07   $928.10   $928.00