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 $59.57   3.338%   $61.5584   $61.56   $61.55   $61.60  
  Purchase #2 $249.93   5.199%   $262.9239   $262.92   $262.90   $262.90  
  Purchase #3 $188.45   4.739%   $197.3806   $197.38   $197.40   $197.40  
  Purchase #4 $110.72   5.737%   $117.072   $117.07   $117.05   $117.10  
  Purchase #5 $220.29   12.675%   $248.2118   $248.21   $248.20   $248.20  
  Purchase #6 $98.34   4.205%   $102.4752   $102.48   $102.50   $102.50  
  Purchase #7 $27.75   6.307%   $29.5002   $29.50   $29.50   $29.50  
  7 purchase totals = $955.05       $1,019.1221   $1,019.12   $1,019.10   $1,019.20