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 $67.51   11.802%   $75.4775   $75.48   $75.50   $75.50  
  Purchase #2 $219.65   7.487%   $236.0952   $236.10   $236.10   $236.10  
  Purchase #3 $136.58   7.559%   $146.9041   $146.90   $146.90   $146.90  
  Purchase #4 $18.54   5.572%   $19.573   $19.57   $19.55   $19.60  
  Purchase #5 $141.75   10.580%   $156.7472   $156.75   $156.75   $156.70  
  Purchase #6 $9.68   13.814%   $11.0172   $11.02   $11.00   $11.00  
  Purchase #7 $24.76   6.174%   $26.2887   $26.29   $26.30   $26.30  
  7 purchase totals = $618.47       $672.1029   $672.11   $672.10   $672.10