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 $146.81   11.159%   $163.1925   $163.19   $163.20   $163.20  
  Purchase #2 $168.41   3.114%   $173.6543   $173.65   $173.65   $173.70  
  Purchase #3 $87.62   3.113%   $90.3476   $90.35   $90.35   $90.30  
  Purchase #4 $67.34   8.857%   $73.3043   $73.30   $73.30   $73.30  
  Purchase #5 $240.33   3.712%   $249.251   $249.25   $249.25   $249.30  
  Purchase #6 $129.38   6.536%   $137.8363   $137.84   $137.85   $137.80  
  Purchase #7 $200.94   8.371%   $217.7607   $217.76   $217.75   $217.80  
  7 purchase totals = $1,040.83       $1,105.3467   $1,105.34   $1,105.35   $1,105.40