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	$42.64	6.420%	$45.3775	$45.38	$45.40	$45.40
Purchase #2	$114.61	8.828%	$124.7278	$124.73	$124.75	$124.70
Purchase #3	$151.48	3.304%	$156.4849	$156.48	$156.50	$156.50
Purchase #4	$228.42	7.192%	$244.848	$244.85	$244.85	$244.80
Purchase #5	$235.31	6.601%	$250.8428	$250.84	$250.85	$250.80
Purchase #6	$6.29	13.792%	$7.1575	$7.16	$7.15	$7.20
Purchase #7	$81.87	12.399%	$92.0211	$92.02	$92.00	$92.00
7 purchase totals =	$860.62		$921.4596	$921.46	$921.50	$921.40