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 $184.45   9.165%   $201.3548   $201.35   $201.35   $201.40  
  Purchase #2 $59.50   13.105%   $67.2975   $67.30   $67.30   $67.30  
  Purchase #3 $60.75   12.461%   $68.3201   $68.32   $68.30   $68.30  
  Purchase #4 $87.49   9.195%   $95.5347   $95.53   $95.55   $95.50  
  Purchase #5 $155.61   11.781%   $173.9424   $173.94   $173.95   $173.90  
  Purchase #6 $76.29   5.430%   $80.4325   $80.43   $80.45   $80.40  
  Purchase #7 $138.92   4.845%   $145.6507   $145.65   $145.65   $145.70  
  7 purchase totals = $763.01       $832.5327   $832.52   $832.55   $832.50