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 $39.71   11.210%   $44.1615   $44.16   $44.15   $44.20  
  Purchase #2 $223.59   5.458%   $235.7935   $235.79   $235.80   $235.80  
  Purchase #3 $76.99   11.737%   $86.0263   $86.03   $86.05   $86.00  
  Purchase #4 $236.91   6.310%   $251.859   $251.86   $251.85   $251.90  
  Purchase #5 $61.53   11.145%   $68.3875   $68.39   $68.40   $68.40  
  Purchase #6 $146.76   13.135%   $166.0369   $166.04   $166.05   $166.00  
  Purchase #7 $65.50   9.203%   $71.528   $71.53   $71.55   $71.50  
  7 purchase totals = $850.99       $923.7927   $923.80   $923.85   $923.80