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 $43.27   12.340%   $48.6095   $48.61   $48.60   $48.60  
  Purchase #2 $215.41   5.230%   $226.6759   $226.68   $226.70   $226.70  
  Purchase #3 $77.56   8.314%   $84.0083   $84.01   $84.00   $84.00  
  Purchase #4 $32.34   4.597%   $33.8267   $33.83   $33.85   $33.80  
  Purchase #5 $39.85   4.463%   $41.6285   $41.63   $41.65   $41.60  
  Purchase #6 $144.47   3.752%   $149.8905   $149.89   $149.90   $149.90  
  Purchase #7 $126.89   6.111%   $134.6442   $134.64   $134.65   $134.60  
  7 purchase totals = $679.79       $719.2836   $719.29   $719.35   $719.20