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 $49.33   13.868%   $56.1711   $56.17   $56.15   $56.20  
  Purchase #2 $108.60   9.848%   $119.2949   $119.29   $119.30   $119.30  
  Purchase #3 $168.83   12.873%   $190.5635   $190.56   $190.55   $190.60  
  Purchase #4 $195.93   7.164%   $209.9664   $209.97   $209.95   $210.00  
  Purchase #5 $211.38   4.448%   $220.7822   $220.78   $220.80   $220.80  
  Purchase #6 $39.58   3.353%   $40.9071   $40.91   $40.90   $40.90  
  Purchase #7 $96.38   6.261%   $102.4144   $102.41   $102.40   $102.40  
  7 purchase totals = $870.03       $940.0996   $940.09   $940.05   $940.20