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 $153.45   13.752%   $174.5524   $174.55   $174.55   $174.60  
  Purchase #2 $245.39   13.436%   $278.3606   $278.36   $278.35   $278.40  
  Purchase #3 $149.79   12.701%   $168.8148   $168.81   $168.80   $168.80  
  Purchase #4 $221.72   7.594%   $238.5574   $238.56   $238.55   $238.60  
  Purchase #5 $67.73   7.213%   $72.6154   $72.62   $72.60   $72.60  
  Purchase #6 $236.60   10.714%   $261.9493   $261.95   $261.95   $261.90  
  Purchase #7 $248.51   4.588%   $259.9116   $259.91   $259.90   $259.90  
  7 purchase totals = $1,323.19       $1,454.7615   $1,454.76   $1,454.70   $1,454.80