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 $247.79   8.605%   $269.1123   $269.11   $269.10   $269.10  
  Purchase #2 $26.32   10.525%   $29.0902   $29.09   $29.10   $29.10  
  Purchase #3 $229.71   10.647%   $254.1672   $254.17   $254.15   $254.20  
  Purchase #4 $57.37   8.585%   $62.2952   $62.30   $62.30   $62.30  
  Purchase #5 $237.96   5.872%   $251.933   $251.93   $251.95   $251.90  
  Purchase #6 $125.36   12.448%   $140.9648   $140.96   $140.95   $141.00  
  Purchase #7 $84.68   4.462%   $88.4584   $88.46   $88.45   $88.50  
  7 purchase totals = $1,009.19       $1,096.0211   $1,096.02   $1,096.00   $1,096.10