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 $87.46   6.615%   $93.2455   $93.25   $93.25   $93.20  
  Purchase #2 $66.44   9.799%   $72.9505   $72.95   $72.95   $73.00  
  Purchase #3 $211.38   3.182%   $218.1061   $218.11   $218.10   $218.10  
  Purchase #4 $79.48   3.423%   $82.2006   $82.20   $82.20   $82.20  
  Purchase #5 $94.50   13.711%   $107.4569   $107.46   $107.45   $107.50  
  Purchase #6 $249.62   5.603%   $263.6062   $263.61   $263.60   $263.60  
  Purchase #7 $111.49   11.467%   $124.2746   $124.27   $124.25   $124.30  
  7 purchase totals = $900.37       $961.8404   $961.85   $961.80   $961.90