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 $71.38   6.828%   $76.2538   $76.25   $76.25   $76.30  
  Purchase #2 $77.46   9.759%   $85.0193   $85.02   $85.00   $85.00  
  Purchase #3 $58.92   12.383%   $66.2161   $66.22   $66.20   $66.20  
  Purchase #4 $140.54   10.758%   $155.6593   $155.66   $155.65   $155.70  
  Purchase #5 $229.65   13.610%   $260.9054   $260.91   $260.90   $260.90  
  Purchase #6 $218.73   10.369%   $241.4101   $241.41   $241.40   $241.40  
  Purchase #7 $23.39   3.442%   $24.1951   $24.20   $24.20   $24.20  
  7 purchase totals = $820.07       $909.6591   $909.67   $909.60   $909.70