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 $86.92   13.556%   $98.7029   $98.70   $98.70   $98.70  
  Purchase #2 $113.61   10.329%   $125.3448   $125.34   $125.35   $125.30  
  Purchase #3 $130.95   3.534%   $135.5778   $135.58   $135.60   $135.60  
  Purchase #4 $163.34   13.720%   $185.7502   $185.75   $185.75   $185.80  
  Purchase #5 $158.31   5.481%   $166.987   $166.99   $167.00   $167.00  
  Purchase #6 $151.92   7.437%   $163.2183   $163.22   $163.20   $163.20  
  Purchase #7 $229.50   8.843%   $249.7947   $249.79   $249.80   $249.80  
  7 purchase totals = $1,034.55       $1,125.3757   $1,125.37   $1,125.40   $1,125.40