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 $234.63   10.608%   $259.5196   $259.52   $259.50   $259.50  
  Purchase #2 $60.55   12.271%   $67.9801   $67.98   $68.00   $68.00  
  Purchase #3 $205.50   3.674%   $213.0501   $213.05   $213.05   $213.10  
  Purchase #4 $9.45   3.547%   $9.7852   $9.79   $9.80   $9.80  
  Purchase #5 $244.95   11.751%   $273.7341   $273.73   $273.75   $273.70  
  Purchase #6 $197.62   9.185%   $215.7714   $215.77   $215.75   $215.80  
  Purchase #7 $112.64   12.669%   $126.9104   $126.91   $126.90   $126.90  
  7 purchase totals = $1,065.34       $1,166.7509   $1,166.75   $1,166.75   $1,166.80