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 $241.56   12.746%   $272.3492   $272.35   $272.35   $272.30  
  Purchase #2 $61.37   10.559%   $67.8501   $67.85   $67.85   $67.90  
  Purchase #3 $92.90   5.475%   $97.9863   $97.99   $98.00   $98.00  
  Purchase #4 $46.41   3.137%   $47.8659   $47.87   $47.85   $47.90  
  Purchase #5 $111.85   4.825%   $117.2468   $117.25   $117.25   $117.20  
  Purchase #6 $216.28   9.343%   $236.487   $236.49   $236.50   $236.50  
  Purchase #7 $68.75   3.382%   $71.0751   $71.08   $71.10   $71.10  
  7 purchase totals = $839.12       $910.8604   $910.88   $910.90   $910.90