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 $86.87   10.461%   $95.9575   $95.96   $95.95   $96.00  
  Purchase #2 $24.91   10.484%   $27.5216   $27.52   $27.50   $27.50  
  Purchase #3 $57.57   12.448%   $64.7363   $64.74   $64.75   $64.70  
  Purchase #4 $188.68   5.603%   $199.2517   $199.25   $199.25   $199.30  
  Purchase #5 $110.32   10.758%   $122.1882   $122.19   $122.20   $122.20  
  Purchase #6 $157.49   12.696%   $177.4849   $177.48   $177.50   $177.50  
  Purchase #7 $22.79   7.483%   $24.4954   $24.50   $24.50   $24.50  
  7 purchase totals = $648.63       $711.6356   $711.64   $711.65   $711.70