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 $47.56   9.452%   $52.0554   $52.06   $52.05   $52.10  
  Purchase #2 $60.44   7.137%   $64.7536   $64.75   $64.75   $64.80  
  Purchase #3 $209.87   9.215%   $229.2095   $229.21   $229.20   $229.20  
  Purchase #4 $158.64   8.854%   $172.686   $172.69   $172.70   $172.70  
  Purchase #5 $11.67   12.806%   $13.1645   $13.16   $13.15   $13.20  
  Purchase #6 $50.82   10.847%   $56.3324   $56.33   $56.35   $56.30  
  Purchase #7 $167.79   7.740%   $180.7769   $180.78   $180.80   $180.80  
  7 purchase totals = $706.79       $768.9783   $768.98   $769.00   $769.10