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	$162.74	5.864%	$172.2831	$172.28	$172.30	$172.30
Purchase #2	$90.88	7.782%	$97.9523	$97.95	$97.95	$98.00
Purchase #3	$46.65	8.829%	$50.7687	$50.77	$50.75	$50.80
Purchase #4	$203.62	13.409%	$230.9234	$230.92	$230.90	$230.90
Purchase #5	$32.28	11.465%	$35.9809	$35.98	$36.00	$36.00
Purchase #6	$40.48	13.286%	$45.8582	$45.86	$45.85	$45.90
Purchase #7	$189.62	3.868%	$196.9545	$196.95	$196.95	$197.00
7 purchase totals =	$766.27		$830.7211	$830.71	$830.70	$830.90