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 $84.49   9.299%   $92.3467   $92.35   $92.35   $92.30  
  Purchase #2 $211.37   6.697%   $225.5254   $225.53   $225.55   $225.50  
  Purchase #3 $237.54   4.677%   $248.6497   $248.65   $248.65   $248.60  
  Purchase #4 $36.71   7.335%   $39.4027   $39.40   $39.40   $39.40  
  Purchase #5 $106.37   6.441%   $113.2213   $113.22   $113.20   $113.20  
  Purchase #6 $131.38   6.226%   $139.5597   $139.56   $139.55   $139.60  
  Purchase #7 $190.44   9.736%   $208.9812   $208.98   $209.00   $209.00  
  7 purchase totals = $998.30       $1,067.6867   $1,067.69   $1,067.70   $1,067.60