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	$197.51	12.285%	$221.7741	$221.77	$221.75	$221.80
Purchase #2	$148.63	9.612%	$162.9163	$162.92	$162.90	$162.90
Purchase #3	$233.51	4.607%	$244.2678	$244.27	$244.25	$244.30
Purchase #4	$164.33	4.303%	$171.4011	$171.40	$171.40	$171.40
Purchase #5	$187.72	9.629%	$205.7956	$205.80	$205.80	$205.80
Purchase #6	$166.50	7.158%	$178.4181	$178.42	$178.40	$178.40
Purchase #7	$33.66	5.738%	$35.5914	$35.59	$35.60	$35.60
7 purchase totals =	$1,131.86		$1,220.1644	$1,220.17	$1,220.10	$1,220.20