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 $239.62   11.498%   $267.1715   $267.17   $267.15   $267.20  
  Purchase #2 $144.98   8.823%   $157.7716   $157.77   $157.75   $157.80  
  Purchase #3 $240.61   7.625%   $258.9565   $258.96   $258.95   $259.00  
  Purchase #4 $47.37   12.223%   $53.16   $53.16   $53.15   $53.20  
  Purchase #5 $93.49   3.300%   $96.5752   $96.58   $96.60   $96.60  
  Purchase #6 $34.74   3.669%   $36.0146   $36.01   $36.00   $36.00  
  Purchase #7 $179.78   9.760%   $197.3265   $197.33   $197.35   $197.30  
  7 purchase totals = $980.59       $1,066.9759   $1,066.98   $1,066.95   $1,067.10