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 $237.51   11.542%   $264.9234   $264.92   $264.90   $264.90  
  Purchase #2 $195.51   12.333%   $219.6222   $219.62   $219.60   $219.60  
  Purchase #3 $187.53   9.456%   $205.2628   $205.26   $205.25   $205.30  
  Purchase #4 $45.84   10.338%   $50.5789   $50.58   $50.60   $50.60  
  Purchase #5 $240.59   4.232%   $250.7718   $250.77   $250.75   $250.80  
  Purchase #6 $34.97   3.682%   $36.2576   $36.26   $36.25   $36.30  
  Purchase #7 $44.77   5.293%   $47.1397   $47.14   $47.15   $47.10  
  7 purchase totals = $986.72       $1,074.5564   $1,074.55   $1,074.50   $1,074.60