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 $61.59   10.727%   $68.1968   $68.20   $68.20   $68.20  
  Purchase #2 $180.91   3.544%   $187.3215   $187.32   $187.30   $187.30  
  Purchase #3 $59.25   12.498%   $66.6551   $66.66   $66.65   $66.70  
  Purchase #4 $84.48   13.162%   $95.5993   $95.60   $95.60   $95.60  
  Purchase #5 $105.55   12.866%   $119.1301   $119.13   $119.15   $119.10  
  Purchase #6 $19.75   9.342%   $21.595   $21.60   $21.60   $21.60  
  Purchase #7 $55.73   10.285%   $61.4618   $61.46   $61.45   $61.50  
  7 purchase totals = $567.26       $619.9596   $619.97   $619.95   $620.00