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 $216.51   13.836%   $246.4663   $246.47   $246.45   $246.50  
  Purchase #2 $112.29   10.494%   $124.0737   $124.07   $124.05   $124.10  
  Purchase #3 $57.60   13.634%   $65.4532   $65.45   $65.45   $65.50  
  Purchase #4 $171.51   12.301%   $192.6074   $192.61   $192.60   $192.60  
  Purchase #5 $14.66   11.172%   $16.2978   $16.30   $16.30   $16.30  
  Purchase #6 $93.97   4.302%   $98.0126   $98.01   $98.00   $98.00  
  Purchase #7 $210.81   3.573%   $218.3422   $218.34   $218.35   $218.30  
  7 purchase totals = $877.35       $961.2532   $961.25   $961.20   $961.30