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 $63.88   8.232%   $69.1386   $69.14   $69.15   $69.10  
  Purchase #2 $220.90   6.344%   $234.9139   $234.91   $234.90   $234.90  
  Purchase #3 $128.31   8.873%   $139.6949   $139.69   $139.70   $139.70  
  Purchase #4 $231.79   12.759%   $261.3641   $261.36   $261.35   $261.40  
  Purchase #5 $118.88   12.280%   $133.4785   $133.48   $133.50   $133.50  
  Purchase #6 $140.62   3.226%   $145.1564   $145.16   $145.15   $145.20  
  Purchase #7 $158.27   5.852%   $167.532   $167.53   $167.55   $167.50  
  7 purchase totals = $1,062.65       $1,151.2784   $1,151.27   $1,151.30   $1,151.30