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 $85.63   3.281%   $88.4395   $88.44   $88.45   $88.40  
  Purchase #2 $105.87   7.829%   $114.1586   $114.16   $114.15   $114.20  
  Purchase #3 $69.45   5.682%   $73.3961   $73.40   $73.40   $73.40  
  Purchase #4 $227.59   4.222%   $237.1988   $237.20   $237.20   $237.20  
  Purchase #5 $82.36   12.214%   $92.4195   $92.42   $92.40   $92.40  
  Purchase #6 $211.46   3.708%   $219.3009   $219.30   $219.30   $219.30  
  Purchase #7 $165.25   13.399%   $187.3918   $187.39   $187.40   $187.40  
  7 purchase totals = $947.61       $1,012.3052   $1,012.31   $1,012.30   $1,012.30