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 $166.73   5.189%   $175.3816   $175.38   $175.40   $175.40  
  Purchase #2 $239.56   10.476%   $264.6563   $264.66   $264.65   $264.70  
  Purchase #3 $94.40   13.424%   $107.0723   $107.07   $107.05   $107.10  
  Purchase #4 $245.64   9.865%   $269.8724   $269.87   $269.85   $269.90  
  Purchase #5 $110.39   13.815%   $125.6404   $125.64   $125.65   $125.60  
  Purchase #6 $47.92   3.864%   $49.7716   $49.77   $49.75   $49.80  
  Purchase #7 $74.80   12.559%   $84.1941   $84.19   $84.20   $84.20  
  7 purchase totals = $979.44       $1,076.5887   $1,076.58   $1,076.55   $1,076.70