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 $58.62   4.574%   $61.3013   $61.30   $61.30   $61.30  
  Purchase #2 $238.97   10.226%   $263.4071   $263.41   $263.40   $263.40  
  Purchase #3 $79.78   5.638%   $84.278   $84.28   $84.30   $84.30  
  Purchase #4 $115.77   11.613%   $129.2144   $129.21   $129.20   $129.20  
  Purchase #5 $41.74   9.528%   $45.717   $45.72   $45.70   $45.70  
  Purchase #6 $129.51   5.693%   $136.883   $136.88   $136.90   $136.90  
  Purchase #7 $236.39   11.512%   $263.6032   $263.60   $263.60   $263.60  
  7 purchase totals = $900.78       $984.4040   $984.40   $984.40   $984.40