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 $248.89   11.166%   $276.6811   $276.68   $276.70   $276.70  
  Purchase #2 $235.38   10.252%   $259.5112   $259.51   $259.50   $259.50  
  Purchase #3 $93.49   5.744%   $98.8601   $98.86   $98.85   $98.90  
  Purchase #4 $162.53   9.842%   $178.5262   $178.53   $178.55   $178.50  
  Purchase #5 $158.40   10.169%   $174.5077   $174.51   $174.50   $174.50  
  Purchase #6 $110.35   12.759%   $124.4296   $124.43   $124.45   $124.40  
  Purchase #7 $10.28   4.441%   $10.7365   $10.74   $10.75   $10.70  
  7 purchase totals = $1,019.32       $1,123.2524   $1,123.26   $1,123.30   $1,123.20