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	$28.33	8.452%	$30.7245	$30.72	$30.70	$30.70
Purchase #2	$144.59	12.233%	$162.2777	$162.28	$162.30	$162.30
Purchase #3	$62.88	13.783%	$71.5468	$71.55	$71.55	$71.50
Purchase #4	$79.91	10.216%	$88.0736	$88.07	$88.05	$88.10
Purchase #5	$164.67	4.664%	$172.3502	$172.35	$172.35	$172.40
Purchase #6	$33.28	12.624%	$37.4813	$37.48	$37.50	$37.50
Purchase #7	$83.64	3.354%	$86.4453	$86.45	$86.45	$86.40
7 purchase totals =	$597.30		$648.8994	$648.90	$648.90	$648.90