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 $68.55   12.689%   $77.2483   $77.25   $77.25   $77.20  
  Purchase #2 $178.46   9.392%   $195.221   $195.22   $195.20   $195.20  
  Purchase #3 $19.78   4.338%   $20.6381   $20.64   $20.65   $20.60  
  Purchase #4 $101.59   11.571%   $113.345   $113.35   $113.35   $113.30  
  Purchase #5 $94.72   9.522%   $103.7392   $103.74   $103.75   $103.70  
  Purchase #6 $94.53   7.622%   $101.7351   $101.74   $101.75   $101.70  
  Purchase #7 $96.47   9.610%   $105.7408   $105.74   $105.75   $105.70  
  7 purchase totals = $654.10       $717.6675   $717.68   $717.70   $717.40