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 $205.86   7.486%   $221.2707   $221.27   $221.25   $221.30  
  Purchase #2 $110.61   11.766%   $123.6244   $123.62   $123.60   $123.60  
  Purchase #3 $24.99   6.144%   $26.5254   $26.53   $26.55   $26.50  
  Purchase #4 $113.80   4.119%   $118.4874   $118.49   $118.50   $118.50  
  Purchase #5 $156.58   3.827%   $162.5723   $162.57   $162.55   $162.60  
  Purchase #6 $233.38   9.132%   $254.6923   $254.69   $254.70   $254.70  
  Purchase #7 $36.42   6.103%   $38.6427   $38.64   $38.65   $38.60  
  7 purchase totals = $881.64       $945.8152   $945.81   $945.80   $945.80