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 $61.38   4.812%   $64.3336   $64.33   $64.35   $64.30  
  Purchase #2 $163.47   11.329%   $181.9895   $181.99   $182.00   $182.00  
  Purchase #3 $90.51   7.635%   $97.4204   $97.42   $97.40   $97.40  
  Purchase #4 $233.61   5.741%   $247.0216   $247.02   $247.00   $247.00  
  Purchase #5 $232.85   11.687%   $260.0632   $260.06   $260.05   $260.10  
  Purchase #6 $61.29   12.139%   $68.73   $68.73   $68.75   $68.70  
  Purchase #7 $51.47   12.776%   $58.0458   $58.05   $58.05   $58.00  
  7 purchase totals = $894.58       $977.6041   $977.60   $977.60   $977.50