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 $231.63   9.641%   $253.9614   $253.96   $253.95   $254.00  
  Purchase #2 $101.62   13.528%   $115.3672   $115.37   $115.35   $115.40  
  Purchase #3 $99.95   10.379%   $110.3238   $110.32   $110.30   $110.30  
  Purchase #4 $157.65   8.849%   $171.6004   $171.60   $171.60   $171.60  
  Purchase #5 $23.34   6.617%   $24.8844   $24.88   $24.90   $24.90  
  Purchase #6 $216.80   13.520%   $246.1114   $246.11   $246.10   $246.10  
  Purchase #7 $89.35   5.822%   $94.552   $94.55   $94.55   $94.60  
  7 purchase totals = $920.34       $1,016.8006   $1,016.79   $1,016.75   $1,016.90