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 $56.38   10.688%   $62.4059   $62.41   $62.40   $62.40  
  Purchase #2 $82.37   5.282%   $86.7208   $86.72   $86.70   $86.70  
  Purchase #3 $187.45   10.744%   $207.5896   $207.59   $207.60   $207.60  
  Purchase #4 $89.31   13.104%   $101.0132   $101.01   $101.00   $101.00  
  Purchase #5 $117.45   5.853%   $124.3243   $124.32   $124.30   $124.30  
  Purchase #6 $122.36   3.263%   $126.3526   $126.35   $126.35   $126.40  
  Purchase #7 $39.71   8.155%   $42.9484   $42.95   $42.95   $42.90  
  7 purchase totals = $695.03       $751.3548   $751.35   $751.30   $751.30