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 $48.82   11.291%   $54.3323   $54.33   $54.35   $54.30  
  Purchase #2 $178.78   5.665%   $188.9079   $188.91   $188.90   $188.90  
  Purchase #3 $201.40   7.361%   $216.2251   $216.23   $216.25   $216.20  
  Purchase #4 $113.80   3.493%   $117.775   $117.78   $117.80   $117.80  
  Purchase #5 $10.66   8.518%   $11.568   $11.57   $11.55   $11.60  
  Purchase #6 $37.34   12.295%   $41.931   $41.93   $41.95   $41.90  
  Purchase #7 $80.67   3.259%   $83.299   $83.30   $83.30   $83.30  
  7 purchase totals = $671.47       $714.0383   $714.05   $714.10   $714.00