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 $56.58   12.361%   $63.5739   $63.57   $63.55   $63.60  
  Purchase #2 $82.56   11.252%   $91.8497   $91.85   $91.85   $91.80  
  Purchase #3 $74.51   6.391%   $79.2719   $79.27   $79.25   $79.30  
  Purchase #4 $72.73   4.820%   $76.2356   $76.24   $76.25   $76.20  
  Purchase #5 $94.87   3.470%   $98.162   $98.16   $98.15   $98.20  
  Purchase #6 $194.48   13.817%   $221.3513   $221.35   $221.35   $221.40  
  Purchase #7 $126.55   8.184%   $136.9069   $136.91   $136.90   $136.90  
  7 purchase totals = $702.28       $767.3513   $767.35   $767.30   $767.40