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	$37.73	11.650%	$42.1255	$42.13	$42.15	$42.10
Purchase #2	$217.34	11.619%	$242.5927	$242.59	$242.60	$242.60
Purchase #3	$54.99	11.580%	$61.3578	$61.36	$61.35	$61.40
Purchase #4	$121.96	4.366%	$127.2848	$127.28	$127.30	$127.30
Purchase #5	$211.59	3.699%	$219.4167	$219.42	$219.40	$219.40
Purchase #6	$49.44	5.397%	$52.1083	$52.11	$52.10	$52.10
Purchase #7	$77.31	3.283%	$79.8481	$79.85	$79.85	$79.80
7 purchase totals =	$770.36		$824.7339	$824.74	$824.75	$824.70