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 $204.40   6.846%   $218.3932   $218.39   $218.40   $218.40  
  Purchase #2 $236.32   12.490%   $265.8364   $265.84   $265.85   $265.80  
  Purchase #3 $153.45   5.756%   $162.2826   $162.28   $162.30   $162.30  
  Purchase #4 $129.62   3.609%   $134.298   $134.30   $134.30   $134.30  
  Purchase #5 $140.63   6.606%   $149.92   $149.92   $149.90   $149.90  
  Purchase #6 $244.30   12.585%   $275.0452   $275.05   $275.05   $275.00  
  Purchase #7 $230.99   13.361%   $261.8526   $261.85   $261.85   $261.90  
  7 purchase totals = $1,339.71       $1,467.6280   $1,467.63   $1,467.65   $1,467.60