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	$11.36	13.422%	$12.8847	$12.88	$12.90	$12.90
Purchase #2	$230.83	8.486%	$250.4182	$250.42	$250.40	$250.40
Purchase #3	$235.71	3.366%	$243.644	$243.64	$243.65	$243.60
Purchase #4	$118.96	3.419%	$123.0272	$123.03	$123.05	$123.00
Purchase #5	$174.96	5.752%	$185.0237	$185.02	$185.00	$185.00
Purchase #6	$179.68	13.359%	$203.6835	$203.68	$203.70	$203.70
Purchase #7	$55.27	7.424%	$59.3732	$59.37	$59.35	$59.40
7 purchase totals =	$1,006.77		$1,078.0545	$1,078.04	$1,078.05	$1,078.00