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 $61.35   13.296%   $69.5071   $69.51   $69.50   $69.50  
  Purchase #2 $103.58   4.583%   $108.3271   $108.33   $108.35   $108.30  
  Purchase #3 $155.50   13.341%   $176.2453   $176.25   $176.25   $176.20  
  Purchase #4 $183.57   7.572%   $197.4699   $197.47   $197.45   $197.50  
  Purchase #5 $80.67   5.707%   $85.2738   $85.27   $85.25   $85.30  
  Purchase #6 $45.44   3.571%   $47.0627   $47.06   $47.05   $47.10  
  Purchase #7 $125.79   6.112%   $133.4783   $133.48   $133.50   $133.50  
  7 purchase totals = $755.90       $817.3642   $817.37   $817.35   $817.40