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	$181.87	3.440%	$188.1263	$188.13	$188.15	$188.10
Purchase #2	$148.63	11.590%	$165.8562	$165.86	$165.85	$165.90
Purchase #3	$18.47	11.231%	$20.5444	$20.54	$20.55	$20.50
Purchase #4	$110.67	11.326%	$123.2045	$123.20	$123.20	$123.20
Purchase #5	$35.72	4.843%	$37.4499	$37.45	$37.45	$37.40
Purchase #6	$5.27	12.504%	$5.929	$5.93	$5.95	$5.90
Purchase #7	$179.98	4.805%	$188.628	$188.63	$188.65	$188.60
7 purchase totals =	$680.61		$729.7383	$729.74	$729.80	$729.60