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 $241.98   9.129%   $264.0704   $264.07   $264.05   $264.10  
  Purchase #2 $250.87   11.196%   $278.9574   $278.96   $278.95   $279.00  
  Purchase #3 $44.67   5.516%   $47.134   $47.13   $47.15   $47.10  
  Purchase #4 $150.55   9.691%   $165.1398   $165.14   $165.15   $165.10  
  Purchase #5 $208.54   9.429%   $228.2032   $228.20   $228.20   $228.20  
  Purchase #6 $174.59   5.160%   $183.5988   $183.60   $183.60   $183.60  
  Purchase #7 $161.94   11.698%   $180.8837   $180.88   $180.90   $180.90  
  7 purchase totals = $1,233.14       $1,347.9873   $1,347.98   $1,348.00   $1,348.00