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	$47.80	12.202%	$53.6326	$53.63	$53.65	$53.60
Purchase #2	$84.38	6.400%	$89.7803	$89.78	$89.80	$89.80
Purchase #3	$57.87	11.496%	$64.5227	$64.52	$64.50	$64.50
Purchase #4	$171.42	11.107%	$190.4596	$190.46	$190.45	$190.50
Purchase #5	$195.93	10.403%	$216.3126	$216.31	$216.30	$216.30
Purchase #6	$11.44	8.690%	$12.4341	$12.43	$12.45	$12.40
Purchase #7	$213.44	9.469%	$233.6506	$233.65	$233.65	$233.70
7 purchase totals =	$782.28		$860.7925	$860.78	$860.80	$860.80