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	$222.29	9.364%	$243.1052	$243.11	$243.10	$243.10
Purchase #2	$111.74	7.786%	$120.4401	$120.44	$120.45	$120.40
Purchase #3	$142.71	7.244%	$153.0479	$153.05	$153.05	$153.00
Purchase #4	$99.95	5.842%	$105.7891	$105.79	$105.80	$105.80
Purchase #5	$104.65	4.581%	$109.444	$109.44	$109.45	$109.40
Purchase #6	$37.39	12.513%	$42.0686	$42.07	$42.05	$42.10
Purchase #7	$239.37	13.730%	$272.2355	$272.24	$272.25	$272.20
7 purchase totals =	$958.10		$1,046.1304	$1,046.14	$1,046.15	$1,046.00