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 $209.44   11.581%   $233.6952   $233.70   $233.70   $233.70  
  Purchase #2 $75.86   8.724%   $82.478   $82.48   $82.50   $82.50  
  Purchase #3 $227.57   12.239%   $255.4223   $255.42   $255.40   $255.40  
  Purchase #4 $236.88   5.587%   $250.1145   $250.11   $250.10   $250.10  
  Purchase #5 $249.77   7.203%   $267.7609   $267.76   $267.75   $267.80  
  Purchase #6 $48.37   11.414%   $53.891   $53.89   $53.90   $53.90  
  Purchase #7 $153.43   10.279%   $169.2011   $169.20   $169.20   $169.20  
  7 purchase totals = $1,201.32       $1,312.5630   $1,312.56   $1,312.55   $1,312.60