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 $59.63   9.318%   $65.1863   $65.19   $65.20   $65.20  
  Purchase #2 $141.64   4.602%   $148.1583   $148.16   $148.15   $148.20  
  Purchase #3 $36.77   8.643%   $39.948   $39.95   $39.95   $39.90  
  Purchase #4 $97.68   7.723%   $105.2238   $105.22   $105.20   $105.20  
  Purchase #5 $25.62   4.871%   $26.868   $26.87   $26.85   $26.90  
  Purchase #6 $54.43   13.601%   $61.833   $61.83   $61.85   $61.80  
  Purchase #7 $200.55   6.177%   $212.938   $212.94   $212.95   $212.90  
  7 purchase totals = $616.32       $660.1554   $660.16   $660.15   $660.10