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	$108.83	3.267%	$112.3855	$112.39	$112.40	$112.40
Purchase #2	$53.58	7.720%	$57.7164	$57.72	$57.70	$57.70
Purchase #3	$121.66	6.426%	$129.4779	$129.48	$129.50	$129.50
Purchase #4	$147.27	3.267%	$152.0813	$152.08	$152.10	$152.10
Purchase #5	$109.43	6.682%	$116.7421	$116.74	$116.75	$116.70
Purchase #6	$160.34	11.660%	$179.0356	$179.04	$179.05	$179.00
Purchase #7	$96.90	3.723%	$100.5076	$100.51	$100.50	$100.50
7 purchase totals =	$798.01		$847.9464	$847.96	$848.00	$847.90