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 $23.84   11.286%   $26.5306   $26.53   $26.55   $26.50  
  Purchase #2 $105.54   5.481%   $111.3246   $111.32   $111.30   $111.30  
  Purchase #3 $166.35   4.759%   $174.2666   $174.27   $174.25   $174.30  
  Purchase #4 $217.60   11.345%   $242.2867   $242.29   $242.30   $242.30  
  Purchase #5 $87.39   4.693%   $91.4912   $91.49   $91.50   $91.50  
  Purchase #6 $104.44   7.727%   $112.5101   $112.51   $112.50   $112.50  
  Purchase #7 $178.95   9.408%   $195.7856   $195.79   $195.80   $195.80  
  7 purchase totals = $884.11       $954.1954   $954.20   $954.20   $954.20