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 $208.39   11.841%   $233.0655   $233.07   $233.05   $233.10  
  Purchase #2 $173.39   6.109%   $183.9824   $183.98   $184.00   $184.00  
  Purchase #3 $124.62   12.239%   $139.8722   $139.87   $139.85   $139.90  
  Purchase #4 $125.77   4.717%   $131.7026   $131.70   $131.70   $131.70  
  Purchase #5 $167.76   11.485%   $187.0272   $187.03   $187.05   $187.00  
  Purchase #6 $27.55   12.482%   $30.9888   $30.99   $31.00   $31.00  
  Purchase #7 $140.98   13.402%   $159.8741   $159.87   $159.85   $159.90  
  7 purchase totals = $968.46       $1,066.5128   $1,066.51   $1,066.50   $1,066.60