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 $57.52   6.558%   $61.2922   $61.29   $61.30   $61.30  
  Purchase #2 $55.51   12.126%   $62.2411   $62.24   $62.25   $62.20  
  Purchase #3 $24.59   7.506%   $26.4357   $26.44   $26.45   $26.40  
  Purchase #4 $55.96   8.739%   $60.8503   $60.85   $60.85   $60.90  
  Purchase #5 $95.73   11.597%   $106.8318   $106.83   $106.85   $106.80  
  Purchase #6 $22.95   4.718%   $24.0328   $24.03   $24.05   $24.00  
  Purchase #7 $173.78   13.870%   $197.8833   $197.88   $197.90   $197.90  
  7 purchase totals = $486.04       $539.5672   $539.56   $539.65   $539.50