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 $222.32   11.341%   $247.5333   $247.53   $247.55   $247.50  
  Purchase #2 $119.31   4.526%   $124.71   $124.71   $124.70   $124.70  
  Purchase #3 $180.32   5.442%   $190.133   $190.13   $190.15   $190.10  
  Purchase #4 $239.74   10.135%   $264.0376   $264.04   $264.05   $264.00  
  Purchase #5 $158.58   4.244%   $165.3101   $165.31   $165.30   $165.30  
  Purchase #6 $222.79   13.243%   $252.2941   $252.29   $252.30   $252.30  
  Purchase #7 $49.99   3.186%   $51.5827   $51.58   $51.60   $51.60  
  7 purchase totals = $1,193.05       $1,295.6008   $1,295.59   $1,295.65   $1,295.50