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	$179.30	3.448%	$185.4823	$185.48	$185.50	$185.50
Purchase #2	$174.92	10.610%	$193.479	$193.48	$193.50	$193.50
Purchase #3	$156.84	3.776%	$162.7623	$162.76	$162.75	$162.80
Purchase #4	$158.82	8.515%	$172.3435	$172.34	$172.35	$172.30
Purchase #5	$42.56	7.398%	$45.7086	$45.71	$45.70	$45.70
Purchase #6	$79.30	12.360%	$89.1015	$89.10	$89.10	$89.10
Purchase #7	$110.94	10.621%	$122.7229	$122.72	$122.70	$122.70
7 purchase totals =	$902.68		$971.6001	$971.59	$971.60	$971.60