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 $249.39   13.157%   $282.2022   $282.20   $282.20   $282.20  
  Purchase #2 $193.77   5.692%   $204.7994   $204.80   $204.80   $204.80  
  Purchase #3 $114.63   6.717%   $122.3297   $122.33   $122.35   $122.30  
  Purchase #4 $208.91   11.549%   $233.037   $233.04   $233.05   $233.00  
  Purchase #5 $127.38   13.731%   $144.8705   $144.87   $144.85   $144.90  
  Purchase #6 $192.71   9.732%   $211.4645   $211.46   $211.45   $211.50  
  Purchase #7 $67.82   3.501%   $70.1944   $70.19   $70.20   $70.20  
  7 purchase totals = $1,154.61       $1,268.8977   $1,268.89   $1,268.90   $1,268.90