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 $69.26   8.777%   $75.339   $75.34   $75.35   $75.30  
  Purchase #2 $249.66   6.738%   $266.4821   $266.48   $266.50   $266.50  
  Purchase #3 $154.66   12.669%   $174.2539   $174.25   $174.25   $174.30  
  Purchase #4 $141.87   5.307%   $149.399   $149.40   $149.40   $149.40  
  Purchase #5 $119.44   13.306%   $135.3327   $135.33   $135.35   $135.30  
  Purchase #6 $246.36   13.652%   $279.9931   $279.99   $280.00   $280.00  
  Purchase #7 $216.41   12.314%   $243.0587   $243.06   $243.05   $243.10  
  7 purchase totals = $1,197.66       $1,323.8585   $1,323.85   $1,323.90   $1,323.90