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 $70.27   4.611%   $73.5101   $73.51   $73.50   $73.50  
  Purchase #2 $208.78   11.321%   $232.416   $232.42   $232.40   $232.40  
  Purchase #3 $57.44   4.730%   $60.1569   $60.16   $60.15   $60.20  
  Purchase #4 $116.91   5.551%   $123.3997   $123.40   $123.40   $123.40  
  Purchase #5 $14.57   6.109%   $15.4601   $15.46   $15.45   $15.50  
  Purchase #6 $192.81   10.835%   $213.701   $213.70   $213.70   $213.70  
  Purchase #7 $87.51   7.471%   $94.0479   $94.05   $94.05   $94.00  
  7 purchase totals = $748.29       $812.6917   $812.70   $812.65   $812.70