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 $81.46   7.435%   $87.5166   $87.52   $87.50   $87.50  
  Purchase #2 $227.91   12.163%   $255.6307   $255.63   $255.65   $255.60  
  Purchase #3 $72.86   5.749%   $77.0487   $77.05   $77.05   $77.00  
  Purchase #4 $56.34   8.548%   $61.1559   $61.16   $61.15   $61.20  
  Purchase #5 $84.56   13.832%   $96.2563   $96.26   $96.25   $96.30  
  Purchase #6 $241.57   12.184%   $271.0029   $271.00   $271.00   $271.00  
  Purchase #7 $130.31   6.711%   $139.0551   $139.06   $139.05   $139.10  
  7 purchase totals = $895.01       $987.6662   $987.68   $987.65   $987.70