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 $224.89   10.827%   $249.2388   $249.24   $249.25   $249.20  
  Purchase #2 $91.36   6.777%   $97.5515   $97.55   $97.55   $97.60  
  Purchase #3 $191.94   9.335%   $209.8576   $209.86   $209.85   $209.90  
  Purchase #4 $159.25   6.489%   $169.5837   $169.58   $169.60   $169.60  
  Purchase #5 $73.39   6.371%   $78.0657   $78.07   $78.05   $78.10  
  Purchase #6 $179.63   4.186%   $187.1493   $187.15   $187.15   $187.10  
  Purchase #7 $77.26   4.281%   $80.5675   $80.57   $80.55   $80.60  
  7 purchase totals = $997.72       $1,072.0141   $1,072.02   $1,072.00   $1,072.10