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 $197.61   10.402%   $218.1654   $218.17   $218.15   $218.20  
  Purchase #2 $21.33   11.634%   $23.8115   $23.81   $23.80   $23.80  
  Purchase #3 $121.99   3.573%   $126.3487   $126.35   $126.35   $126.30  
  Purchase #4 $206.61   13.233%   $233.9507   $233.95   $233.95   $234.00  
  Purchase #5 $164.35   5.524%   $173.4287   $173.43   $173.45   $173.40  
  Purchase #6 $5.76   4.290%   $6.0071   $6.01   $6.00   $6.00  
  Purchase #7 $88.39   12.868%   $99.764   $99.76   $99.75   $99.80  
  7 purchase totals = $806.04       $881.4761   $881.48   $881.45   $881.50