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	$95.59	6.616%	$101.9142	$101.91	$101.90	$101.90
Purchase #2	$134.63	8.304%	$145.8097	$145.81	$145.80	$145.80
Purchase #3	$33.31	6.595%	$35.5068	$35.51	$35.50	$35.50
Purchase #4	$150.91	11.266%	$167.9115	$167.91	$167.90	$167.90
Purchase #5	$209.46	6.681%	$223.454	$223.45	$223.45	$223.50
Purchase #6	$90.42	8.811%	$98.3869	$98.39	$98.40	$98.40
Purchase #7	$196.26	9.649%	$215.1971	$215.20	$215.20	$215.20
7 purchase totals =	$910.58		$988.1802	$988.18	$988.15	$988.20