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	$234.50	3.328%	$242.3042	$242.30	$242.30	$242.30
Purchase #2	$247.35	7.392%	$265.6341	$265.63	$265.65	$265.60
Purchase #3	$81.33	9.462%	$89.0254	$89.03	$89.05	$89.00
Purchase #4	$89.33	13.389%	$101.2904	$101.29	$101.30	$101.30
Purchase #5	$54.39	6.845%	$58.113	$58.11	$58.10	$58.10
Purchase #6	$228.56	4.182%	$238.1184	$238.12	$238.10	$238.10
Purchase #7	$115.90	6.438%	$123.3616	$123.36	$123.35	$123.40
7 purchase totals =	$1,051.36		$1,117.8471	$1,117.84	$1,117.85	$1,117.80