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 $208.81   3.208%   $215.5086   $215.51   $215.50   $215.50  
  Purchase #2 $79.98   9.344%   $87.4533   $87.45   $87.45   $87.50  
  Purchase #3 $128.39   9.118%   $140.0966   $140.10   $140.10   $140.10  
  Purchase #4 $23.83   10.663%   $26.371   $26.37   $26.35   $26.40  
  Purchase #5 $108.52   8.830%   $118.1023   $118.10   $118.10   $118.10  
  Purchase #6 $106.70   11.480%   $118.9492   $118.95   $118.95   $118.90  
  Purchase #7 $224.83   9.181%   $245.4716   $245.47   $245.45   $245.50  
  7 purchase totals = $881.06       $951.9526   $951.95   $951.90   $952.00