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 $232.66   13.581%   $264.2576   $264.26   $264.25   $264.30  
  Purchase #2 $229.48   8.743%   $249.5434   $249.54   $249.55   $249.50  
  Purchase #3 $197.60   8.674%   $214.7398   $214.74   $214.75   $214.70  
  Purchase #4 $101.34   12.873%   $114.3855   $114.39   $114.40   $114.40  
  Purchase #5 $52.66   8.869%   $57.3304   $57.33   $57.35   $57.30  
  Purchase #6 $140.98   7.701%   $151.8369   $151.84   $151.85   $151.80  
  Purchase #7 $5.62   4.368%   $5.8655   $5.87   $5.85   $5.90  
  7 purchase totals = $960.34       $1,057.9591   $1,057.97   $1,058.00   $1,057.90