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 $162.76   8.383%   $176.4042   $176.40   $176.40   $176.40  
  Purchase #2 $61.78   13.199%   $69.9343   $69.93   $69.95   $69.90  
  Purchase #3 $205.93   7.453%   $221.278   $221.28   $221.30   $221.30  
  Purchase #4 $12.99   11.322%   $14.4607   $14.46   $14.45   $14.50  
  Purchase #5 $233.71   5.344%   $246.1995   $246.20   $246.20   $246.20  
  Purchase #6 $105.86   13.731%   $120.3956   $120.40   $120.40   $120.40  
  Purchase #7 $115.38   7.243%   $123.737   $123.74   $123.75   $123.70  
  7 purchase totals = $898.41       $972.4093   $972.41   $972.45   $972.40