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 $213.28   5.563%   $225.1448   $225.14   $225.15   $225.10  
  Purchase #2 $93.99   13.717%   $106.8826   $106.88   $106.90   $106.90  
  Purchase #3 $26.75   6.781%   $28.5639   $28.56   $28.55   $28.60  
  Purchase #4 $76.61   8.436%   $83.0728   $83.07   $83.05   $83.10  
  Purchase #5 $41.86   11.355%   $46.6132   $46.61   $46.60   $46.60  
  Purchase #6 $236.65   9.393%   $258.8785   $258.88   $258.90   $258.90  
  Purchase #7 $189.97   6.680%   $202.66   $202.66   $202.65   $202.70  
  7 purchase totals = $879.11       $951.8158   $951.80   $951.80   $951.90