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 $61.92   8.159%   $66.9721   $66.97   $66.95   $67.00  
  Purchase #2 $138.55   3.417%   $143.2843   $143.28   $143.30   $143.30  
  Purchase #3 $241.37   4.852%   $253.0813   $253.08   $253.10   $253.10  
  Purchase #4 $61.93   3.826%   $64.2994   $64.30   $64.30   $64.30  
  Purchase #5 $79.50   13.633%   $90.3382   $90.34   $90.35   $90.30  
  Purchase #6 $132.95   3.303%   $137.3413   $137.34   $137.35   $137.30  
  Purchase #7 $56.32   13.252%   $63.7835   $63.78   $63.80   $63.80  
  7 purchase totals = $772.54       $819.1001   $819.09   $819.15   $819.10