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 $56.93   9.170%   $62.1505   $62.15   $62.15   $62.20  
  Purchase #2 $40.52   9.143%   $44.2247   $44.22   $44.20   $44.20  
  Purchase #3 $131.60   7.661%   $141.6819   $141.68   $141.70   $141.70  
  Purchase #4 $86.92   3.386%   $89.8631   $89.86   $89.85   $89.90  
  Purchase #5 $46.25   5.827%   $48.945   $48.95   $48.95   $48.90  
  Purchase #6 $23.25   10.474%   $25.6852   $25.69   $25.70   $25.70  
  Purchase #7 $184.61   6.807%   $197.1764   $197.18   $197.20   $197.20  
  7 purchase totals = $570.08       $609.7268   $609.73   $609.75   $609.80