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 $201.95   11.776%   $225.7316   $225.73   $225.75   $225.70  
  Purchase #2 $60.85   11.288%   $67.7187   $67.72   $67.70   $67.70  
  Purchase #3 $112.42   13.312%   $127.3854   $127.39   $127.40   $127.40  
  Purchase #4 $207.87   6.784%   $221.9719   $221.97   $221.95   $222.00  
  Purchase #5 $173.73   10.112%   $191.2976   $191.30   $191.30   $191.30  
  Purchase #6 $217.91   4.127%   $226.9031   $226.90   $226.90   $226.90  
  Purchase #7 $240.89   3.647%   $249.6753   $249.68   $249.70   $249.70  
  7 purchase totals = $1,215.62       $1,310.6836   $1,310.69   $1,310.70   $1,310.70