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 $93.95   3.642%   $97.3717   $97.37   $97.35   $97.40  
  Purchase #2 $96.29   5.523%   $101.6081   $101.61   $101.60   $101.60  
  Purchase #3 $97.41   3.397%   $100.719   $100.72   $100.70   $100.70  
  Purchase #4 $45.78   3.234%   $47.2605   $47.26   $47.25   $47.30  
  Purchase #5 $14.32   11.756%   $16.0035   $16.00   $16.00   $16.00  
  Purchase #6 $111.75   6.441%   $118.9478   $118.95   $118.95   $118.90  
  Purchase #7 $114.74   3.246%   $118.4645   $118.46   $118.45   $118.50  
  7 purchase totals = $574.24       $600.3751   $600.37   $600.30   $600.40