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 $63.32   12.174%   $71.0286   $71.03   $71.05   $71.00  
  Purchase #2 $59.78   8.620%   $64.933   $64.93   $64.95   $64.90  
  Purchase #3 $117.30   13.841%   $133.5355   $133.54   $133.55   $133.50  
  Purchase #4 $91.40   7.386%   $98.1508   $98.15   $98.15   $98.20  
  Purchase #5 $110.71   3.605%   $114.7011   $114.70   $114.70   $114.70  
  Purchase #6 $192.88   6.844%   $206.0807   $206.08   $206.10   $206.10  
  Purchase #7 $172.94   12.327%   $194.2583   $194.26   $194.25   $194.30  
  7 purchase totals = $808.33       $882.6880   $882.69   $882.75   $882.70