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 $247.99   6.347%   $263.7299   $263.73   $263.75   $263.70  
  Purchase #2 $219.64   5.817%   $232.4165   $232.42   $232.40   $232.40  
  Purchase #3 $23.68   11.537%   $26.412   $26.41   $26.40   $26.40  
  Purchase #4 $70.58   11.563%   $78.7412   $78.74   $78.75   $78.70  
  Purchase #5 $202.97   11.830%   $226.9814   $226.98   $227.00   $227.00  
  Purchase #6 $214.56   6.667%   $228.8647   $228.86   $228.85   $228.90  
  Purchase #7 $207.46   8.190%   $224.451   $224.45   $224.45   $224.50  
  7 purchase totals = $1,186.88       $1,281.5967   $1,281.59   $1,281.60   $1,281.60