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	$6.36	7.726%	$6.8514	$6.85	$6.85	$6.90
Purchase #2	$204.56	9.286%	$223.5554	$223.56	$223.55	$223.60
Purchase #3	$232.25	4.478%	$242.6502	$242.65	$242.65	$242.70
Purchase #4	$223.32	11.318%	$248.5954	$248.60	$248.60	$248.60
Purchase #5	$137.60	5.328%	$144.9313	$144.93	$144.95	$144.90
Purchase #6	$89.92	10.851%	$99.6772	$99.68	$99.70	$99.70
Purchase #7	$74.35	9.331%	$81.2876	$81.29	$81.30	$81.30
7 purchase totals =	$968.36		$1,047.5485	$1,047.56	$1,047.60	$1,047.70