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 $232.33   8.397%   $251.8388   $251.84   $251.85   $251.80  
  Purchase #2 $208.77   6.476%   $222.2899   $222.29   $222.30   $222.30  
  Purchase #3 $33.39   13.427%   $37.8733   $37.87   $37.85   $37.90  
  Purchase #4 $46.54   12.398%   $52.31   $52.31   $52.30   $52.30  
  Purchase #5 $237.79   6.526%   $253.3082   $253.31   $253.30   $253.30  
  Purchase #6 $208.40   13.736%   $237.0258   $237.03   $237.05   $237.00  
  Purchase #7 $194.82   5.723%   $205.9695   $205.97   $205.95   $206.00  
  7 purchase totals = $1,162.04       $1,260.6155   $1,260.62   $1,260.60   $1,260.60