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 $227.69   4.633%   $238.2389   $238.24   $238.25   $238.20  
  Purchase #2 $248.39   12.149%   $278.5669   $278.57   $278.55   $278.60  
  Purchase #3 $59.82   7.205%   $64.13   $64.13   $64.15   $64.10  
  Purchase #4 $212.30   7.238%   $227.6663   $227.67   $227.65   $227.70  
  Purchase #5 $220.88   5.621%   $233.2957   $233.30   $233.30   $233.30  
  Purchase #6 $116.51   6.755%   $124.3803   $124.38   $124.40   $124.40  
  Purchase #7 $49.90   9.247%   $54.5143   $54.51   $54.50   $54.50  
  7 purchase totals = $1,135.49       $1,220.7924   $1,220.80   $1,220.80   $1,220.80