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	$55.77	6.340%	$59.3058	$59.31	$59.30	$59.30
Purchase #2	$227.85	9.842%	$250.275	$250.28	$250.30	$250.30
Purchase #3	$172.37	9.853%	$189.3536	$189.35	$189.35	$189.40
Purchase #4	$45.33	12.465%	$50.9804	$50.98	$51.00	$51.00
Purchase #5	$189.51	9.433%	$207.3865	$207.39	$207.40	$207.40
Purchase #6	$192.78	6.713%	$205.7213	$205.72	$205.70	$205.70
Purchase #7	$26.49	3.399%	$27.3904	$27.39	$27.40	$27.40
7 purchase totals =	$910.10		$990.4130	$990.42	$990.45	$990.50