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 $232.98   5.261%   $245.2371   $245.24   $245.25   $245.20  
  Purchase #2 $20.97   7.604%   $22.5646   $22.56   $22.55   $22.60  
  Purchase #3 $51.51   6.823%   $55.0245   $55.02   $55.00   $55.00  
  Purchase #4 $71.75   9.558%   $78.6079   $78.61   $78.60   $78.60  
  Purchase #5 $64.36   13.824%   $73.2571   $73.26   $73.25   $73.30  
  Purchase #6 $238.29   12.460%   $267.9809   $267.98   $268.00   $268.00  
  Purchase #7 $231.99   5.589%   $244.9559   $244.96   $244.95   $245.00  
  7 purchase totals = $911.85       $987.6280   $987.63   $987.60   $987.70