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 $25.88   3.641%   $26.8223   $26.82   $26.80   $26.80  
  Purchase #2 $246.61   7.711%   $265.6261   $265.63   $265.65   $265.60  
  Purchase #3 $90.42   7.790%   $97.4637   $97.46   $97.45   $97.50  
  Purchase #4 $197.71   7.345%   $212.2318   $212.23   $212.25   $212.20  
  Purchase #5 $236.68   12.839%   $267.0673   $267.07   $267.05   $267.10  
  Purchase #6 $205.54   10.864%   $227.8699   $227.87   $227.85   $227.90  
  Purchase #7 $107.86   13.606%   $122.5354   $122.54   $122.55   $122.50  
  7 purchase totals = $1,110.70       $1,219.6165   $1,219.62   $1,219.60   $1,219.60