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 $41.70   13.569%   $47.3583   $47.36   $47.35   $47.40  
  Purchase #2 $244.89   11.403%   $272.8148   $272.81   $272.80   $272.80  
  Purchase #3 $165.54   11.341%   $184.3139   $184.31   $184.30   $184.30  
  Purchase #4 $57.81   10.147%   $63.676   $63.68   $63.70   $63.70  
  Purchase #5 $82.59   9.188%   $90.1784   $90.18   $90.20   $90.20  
  Purchase #6 $105.34   10.201%   $116.0857   $116.09   $116.10   $116.10  
  Purchase #7 $246.66   5.825%   $261.0279   $261.03   $261.05   $261.00  
  7 purchase totals = $944.53       $1,035.4550   $1,035.46   $1,035.50   $1,035.50