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	$32.51	9.601%	$35.6313	$35.63	$35.65	$35.60
Purchase #2	$160.78	4.745%	$168.409	$168.41	$168.40	$168.40
Purchase #3	$132.73	11.219%	$147.621	$147.62	$147.60	$147.60
Purchase #4	$156.57	6.520%	$166.7784	$166.78	$166.80	$166.80
Purchase #5	$24.40	3.570%	$25.2711	$25.27	$25.25	$25.30
Purchase #6	$11.54	13.581%	$13.1072	$13.11	$13.10	$13.10
Purchase #7	$36.92	5.351%	$38.8956	$38.90	$38.90	$38.90
7 purchase totals =	$555.45		$595.7136	$595.72	$595.70	$595.70