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 $46.42   13.362%   $52.6226   $52.62   $52.60   $52.60  
  Purchase #2 $232.72   12.470%   $261.7402   $261.74   $261.75   $261.70  
  Purchase #3 $245.58   12.318%   $275.8305   $275.83   $275.85   $275.80  
  Purchase #4 $226.56   9.836%   $248.8444   $248.84   $248.85   $248.80  
  Purchase #5 $125.64   13.688%   $142.8376   $142.84   $142.85   $142.80  
  Purchase #6 $38.94   4.420%   $40.6611   $40.66   $40.65   $40.70  
  Purchase #7 $138.49   7.102%   $148.3256   $148.33   $148.35   $148.30  
  7 purchase totals = $1,054.35       $1,170.8620   $1,170.86   $1,170.90   $1,170.70