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	$32.32	9.512%	$35.3943	$35.39	$35.40	$35.40
Purchase #2	$196.51	8.447%	$213.1092	$213.11	$213.10	$213.10
Purchase #3	$243.27	4.793%	$254.9299	$254.93	$254.95	$254.90
Purchase #4	$126.25	4.769%	$132.2709	$132.27	$132.25	$132.30
Purchase #5	$117.50	8.687%	$127.7072	$127.71	$127.70	$127.70
Purchase #6	$40.36	3.855%	$41.9159	$41.92	$41.90	$41.90
Purchase #7	$80.83	10.370%	$89.2121	$89.21	$89.20	$89.20
7 purchase totals =	$837.04		$894.5395	$894.54	$894.50	$894.50