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 $201.63   13.549%   $228.9488   $228.95   $228.95   $228.90  
  Purchase #2 $19.78   4.629%   $20.6956   $20.70   $20.70   $20.70  
  Purchase #3 $216.32   3.171%   $223.1795   $223.18   $223.20   $223.20  
  Purchase #4 $74.38   3.769%   $77.1834   $77.18   $77.20   $77.20  
  Purchase #5 $62.43   6.719%   $66.6247   $66.62   $66.60   $66.60  
  Purchase #6 $42.81   4.781%   $44.8567   $44.86   $44.85   $44.90  
  Purchase #7 $86.35   6.548%   $92.0042   $92.00   $92.00   $92.00  
  7 purchase totals = $703.70       $753.4929   $753.49   $753.50   $753.50