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	$170.67	8.715%	$185.5439	$185.54	$185.55	$185.50
Purchase #2	$224.30	7.621%	$241.3939	$241.39	$241.40	$241.40
Purchase #3	$212.84	9.479%	$233.0151	$233.02	$233.00	$233.00
Purchase #4	$10.37	9.550%	$11.3603	$11.36	$11.35	$11.40
Purchase #5	$90.78	9.715%	$99.5993	$99.60	$99.60	$99.60
Purchase #6	$159.31	13.640%	$181.0399	$181.04	$181.05	$181.00
Purchase #7	$137.79	5.514%	$145.3877	$145.39	$145.40	$145.40
7 purchase totals =	$1,006.06		$1,097.3401	$1,097.34	$1,097.35	$1,097.30