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	$153.74	12.585%	$173.0882	$173.09	$173.10	$173.10
Purchase #2	$221.60	10.739%	$245.3976	$245.40	$245.40	$245.40
Purchase #3	$155.63	7.187%	$166.8151	$166.82	$166.80	$166.80
Purchase #4	$117.46	11.782%	$131.2991	$131.30	$131.30	$131.30
Purchase #5	$179.84	8.174%	$194.5401	$194.54	$194.55	$194.50
Purchase #6	$82.41	8.133%	$89.1124	$89.11	$89.10	$89.10
Purchase #7	$68.49	3.712%	$71.0323	$71.03	$71.05	$71.00
7 purchase totals =	$979.17		$1,071.2848	$1,071.29	$1,071.30	$1,071.20