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 $63.97   6.223%   $67.9509   $67.95   $67.95   $68.00  
  Purchase #2 $207.63   7.438%   $223.0735   $223.07   $223.05   $223.10  
  Purchase #3 $34.99   7.318%   $37.5506   $37.55   $37.55   $37.60  
  Purchase #4 $187.79   3.762%   $194.8547   $194.85   $194.85   $194.90  
  Purchase #5 $69.55   4.107%   $72.4064   $72.41   $72.40   $72.40  
  Purchase #6 $19.80   10.550%   $21.8889   $21.89   $21.90   $21.90  
  Purchase #7 $54.82   3.384%   $56.6751   $56.68   $56.70   $56.70  
  7 purchase totals = $638.55       $674.4001   $674.40   $674.40   $674.60