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 $224.41   5.137%   $235.9379   $235.94   $235.95   $235.90  
  Purchase #2 $112.62   10.375%   $124.3043   $124.30   $124.30   $124.30  
  Purchase #3 $162.37   13.427%   $184.1714   $184.17   $184.15   $184.20  
  Purchase #4 $141.70   12.589%   $159.5386   $159.54   $159.55   $159.50  
  Purchase #5 $207.80   6.646%   $221.6104   $221.61   $221.60   $221.60  
  Purchase #6 $70.46   8.293%   $76.3032   $76.30   $76.30   $76.30  
  Purchase #7 $223.75   12.561%   $251.8552   $251.86   $251.85   $251.90  
  7 purchase totals = $1,143.11       $1,253.7210   $1,253.72   $1,253.70   $1,253.70