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 $114.97   10.206%   $126.7038   $126.70   $126.70   $126.70  
  Purchase #2 $149.28   11.619%   $166.6248   $166.62   $166.60   $166.60  
  Purchase #3 $25.84   9.345%   $28.2547   $28.25   $28.25   $28.30  
  Purchase #4 $233.90   9.121%   $255.234   $255.23   $255.25   $255.20  
  Purchase #5 $20.38   6.164%   $21.6362   $21.64   $21.65   $21.60  
  Purchase #6 $165.51   13.118%   $187.2216   $187.22   $187.20   $187.20  
  Purchase #7 $118.60   10.170%   $130.6616   $130.66   $130.65   $130.70  
  7 purchase totals = $828.48       $916.3367   $916.32   $916.30   $916.30