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	$49.31	12.557%	$55.5019	$55.50	$55.50	$55.50
Purchase #2	$39.28	13.506%	$44.5852	$44.59	$44.60	$44.60
Purchase #3	$153.66	9.862%	$168.8139	$168.81	$168.80	$168.80
Purchase #4	$180.51	5.468%	$190.3803	$190.38	$190.40	$190.40
Purchase #5	$152.43	4.479%	$159.2573	$159.26	$159.25	$159.30
Purchase #6	$26.25	8.825%	$28.5666	$28.57	$28.55	$28.60
Purchase #7	$168.61	8.490%	$182.925	$182.93	$182.95	$182.90
7 purchase totals =	$770.05		$830.0302	$830.04	$830.05	$830.10