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 $14.53   13.469%   $16.487   $16.49   $16.50   $16.50  
  Purchase #2 $60.33   3.644%   $62.5284   $62.53   $62.55   $62.50  
  Purchase #3 $71.26   4.372%   $74.3755   $74.38   $74.40   $74.40  
  Purchase #4 $193.61   9.324%   $211.6622   $211.66   $211.65   $211.70  
  Purchase #5 $40.92   8.436%   $44.372   $44.37   $44.35   $44.40  
  Purchase #6 $39.80   10.825%   $44.1084   $44.11   $44.10   $44.10  
  Purchase #7 $194.73   13.169%   $220.374   $220.37   $220.35   $220.40  
  7 purchase totals = $615.18       $673.9075   $673.91   $673.90   $674.00