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 $60.48   12.704%   $68.1634   $68.16   $68.15   $68.20  
  Purchase #2 $63.63   9.503%   $69.6768   $69.68   $69.70   $69.70  
  Purchase #3 $207.31   13.466%   $235.2264   $235.23   $235.25   $235.20  
  Purchase #4 $111.85   9.590%   $122.5764   $122.58   $122.60   $122.60  
  Purchase #5 $184.70   13.425%   $209.496   $209.50   $209.50   $209.50  
  Purchase #6 $14.33   11.262%   $15.9438   $15.94   $15.95   $15.90  
  Purchase #7 $14.93   9.478%   $16.3451   $16.35   $16.35   $16.30  
  7 purchase totals = $657.23       $737.4279   $737.44   $737.50   $737.40