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 $104.41   11.456%   $116.3712   $116.37   $116.35   $116.40  
  Purchase #2 $172.83   9.799%   $189.7656   $189.77   $189.75   $189.80  
  Purchase #3 $30.84   7.796%   $33.2443   $33.24   $33.25   $33.20  
  Purchase #4 $205.84   13.302%   $233.2208   $233.22   $233.20   $233.20  
  Purchase #5 $224.58   10.865%   $248.9806   $248.98   $249.00   $249.00  
  Purchase #6 $140.25   4.744%   $146.9035   $146.90   $146.90   $146.90  
  Purchase #7 $69.26   8.644%   $75.2468   $75.25   $75.25   $75.20  
  7 purchase totals = $948.01       $1,043.7328   $1,043.73   $1,043.70   $1,043.70