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 $167.55   8.785%   $182.2693   $182.27   $182.25   $182.30  
  Purchase #2 $35.84   7.340%   $38.4707   $38.47   $38.45   $38.50  
  Purchase #3 $25.72   12.596%   $28.9597   $28.96   $28.95   $29.00  
  Purchase #4 $229.86   9.121%   $250.8255   $250.83   $250.85   $250.80  
  Purchase #5 $104.98   12.430%   $118.029   $118.03   $118.05   $118.00  
  Purchase #6 $216.28   8.514%   $234.6941   $234.69   $234.70   $234.70  
  Purchase #7 $81.78   12.454%   $91.9649   $91.96   $91.95   $92.00  
  7 purchase totals = $862.01       $945.2132   $945.21   $945.20   $945.30