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	$18.56	11.198%	$20.6383	$20.64	$20.65	$20.60
Purchase #2	$133.91	7.739%	$144.2733	$144.27	$144.25	$144.30
Purchase #3	$173.98	11.197%	$193.4605	$193.46	$193.45	$193.50
Purchase #4	$98.36	7.560%	$105.796	$105.80	$105.80	$105.80
Purchase #5	$203.73	9.436%	$222.954	$222.95	$222.95	$223.00
Purchase #6	$145.96	9.648%	$160.0422	$160.04	$160.05	$160.00
Purchase #7	$79.48	12.510%	$89.4229	$89.42	$89.40	$89.40
7 purchase totals =	$853.98		$936.5872	$936.58	$936.55	$936.60