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 $221.68   9.742%   $243.2761   $243.28   $243.30   $243.30  
  Purchase #2 $187.57   5.295%   $197.5018   $197.50   $197.50   $197.50  
  Purchase #3 $211.48   11.779%   $236.3902   $236.39   $236.40   $236.40  
  Purchase #4 $26.45   5.656%   $27.946   $27.95   $27.95   $27.90  
  Purchase #5 $228.32   6.781%   $243.8024   $243.80   $243.80   $243.80  
  Purchase #6 $86.71   6.623%   $92.4528   $92.45   $92.45   $92.50  
  Purchase #7 $28.37   4.872%   $29.7522   $29.75   $29.75   $29.80  
  7 purchase totals = $990.58       $1,071.1215   $1,071.12   $1,071.15   $1,071.20