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	$37.93	11.213%	$42.1831	$42.18	$42.20	$42.20
Purchase #2	$130.28	10.113%	$143.4552	$143.46	$143.45	$143.50
Purchase #3	$215.41	13.399%	$244.2728	$244.27	$244.25	$244.30
Purchase #4	$59.44	11.651%	$66.3654	$66.37	$66.35	$66.40
Purchase #5	$166.73	6.364%	$177.3407	$177.34	$177.35	$177.30
Purchase #6	$188.89	12.693%	$212.8658	$212.87	$212.85	$212.90
Purchase #7	$206.45	10.384%	$227.8878	$227.89	$227.90	$227.90
7 purchase totals =	$1,005.13		$1,114.3708	$1,114.38	$1,114.35	$1,114.50