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 $72.61   3.228%   $74.9539   $74.95   $74.95   $75.00  
  Purchase #2 $193.92   4.792%   $203.2126   $203.21   $203.20   $203.20  
  Purchase #3 $58.97   9.790%   $64.7432   $64.74   $64.75   $64.70  
  Purchase #4 $65.49   3.818%   $67.9904   $67.99   $68.00   $68.00  
  Purchase #5 $69.59   11.416%   $77.5344   $77.53   $77.55   $77.50  
  Purchase #6 $203.28   4.694%   $212.822   $212.82   $212.80   $212.80  
  Purchase #7 $134.41   8.677%   $146.0728   $146.07   $146.05   $146.10  
  7 purchase totals = $798.27       $847.3293   $847.31   $847.30   $847.30