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 $147.64   3.189%   $152.3482   $152.35   $152.35   $152.30  
  Purchase #2 $188.87   11.670%   $210.9111   $210.91   $210.90   $210.90  
  Purchase #3 $51.46   9.737%   $56.4707   $56.47   $56.45   $56.50  
  Purchase #4 $23.36   6.202%   $24.8088   $24.81   $24.80   $24.80  
  Purchase #5 $21.38   13.354%   $24.2351   $24.24   $24.25   $24.20  
  Purchase #6 $54.86   13.326%   $62.1706   $62.17   $62.15   $62.20  
  Purchase #7 $227.32   3.657%   $235.6331   $235.63   $235.65   $235.60  
  7 purchase totals = $714.89       $766.5776   $766.58   $766.55   $766.50