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 $120.67   3.606%   $125.0214   $125.02   $125.00   $125.00  
  Purchase #2 $30.62   4.365%   $31.9566   $31.96   $31.95   $32.00  
  Purchase #3 $150.85   4.546%   $157.7076   $157.71   $157.70   $157.70  
  Purchase #4 $52.48   12.352%   $58.9623   $58.96   $58.95   $59.00  
  Purchase #5 $228.81   13.817%   $260.4247   $260.42   $260.40   $260.40  
  Purchase #6 $229.93   9.332%   $251.3871   $251.39   $251.40   $251.40  
  Purchase #7 $43.77   10.862%   $48.5243   $48.52   $48.50   $48.50  
  7 purchase totals = $857.13       $933.9840   $933.98   $933.90   $934.00