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 $89.87   3.210%   $92.7548   $92.75   $92.75   $92.80  
  Purchase #2 $131.53   5.659%   $138.9733   $138.97   $138.95   $139.00  
  Purchase #3 $55.92   5.469%   $58.9783   $58.98   $59.00   $59.00  
  Purchase #4 $56.87   8.522%   $61.7165   $61.72   $61.70   $61.70  
  Purchase #5 $118.59   3.278%   $122.4774   $122.48   $122.50   $122.50  
  Purchase #6 $167.85   3.733%   $174.1158   $174.12   $174.10   $174.10  
  Purchase #7 $204.78   13.709%   $232.8533   $232.85   $232.85   $232.90  
  7 purchase totals = $825.41       $881.8694   $881.87   $881.85   $882.00