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 $30.82   12.419%   $34.6475   $34.65   $34.65   $34.60  
  Purchase #2 $91.93   10.602%   $101.6764   $101.68   $101.70   $101.70  
  Purchase #3 $236.80   4.522%   $247.5081   $247.51   $247.50   $247.50  
  Purchase #4 $181.28   9.368%   $198.2623   $198.26   $198.25   $198.30  
  Purchase #5 $77.35   4.243%   $80.632   $80.63   $80.65   $80.60  
  Purchase #6 $21.29   5.240%   $22.4056   $22.41   $22.40   $22.40  
  Purchase #7 $97.57   10.816%   $108.1232   $108.12   $108.10   $108.10  
  7 purchase totals = $737.04       $793.2551   $793.26   $793.25   $793.20