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	$73.41	7.781%	$79.122	$79.12	$79.10	$79.10
Purchase #2	$227.81	13.274%	$258.0495	$258.05	$258.05	$258.00
Purchase #3	$83.37	10.281%	$91.9413	$91.94	$91.95	$91.90
Purchase #4	$10.53	7.501%	$11.3199	$11.32	$11.30	$11.30
Purchase #5	$243.27	10.341%	$268.4266	$268.43	$268.45	$268.40
Purchase #6	$112.36	9.755%	$123.3207	$123.32	$123.30	$123.30
Purchase #7	$117.68	8.157%	$127.2792	$127.28	$127.30	$127.30
7 purchase totals =	$868.43		$959.4592	$959.46	$959.45	$959.30