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	$122.78	6.200%	$130.3924	$130.39	$130.40	$130.40
Purchase #2	$152.43	3.273%	$157.419	$157.42	$157.40	$157.40
Purchase #3	$83.49	11.255%	$92.8868	$92.89	$92.90	$92.90
Purchase #4	$218.67	5.442%	$230.57	$230.57	$230.55	$230.60
Purchase #5	$132.61	7.164%	$142.1102	$142.11	$142.10	$142.10
Purchase #6	$53.95	13.612%	$61.2937	$61.29	$61.30	$61.30
Purchase #7	$231.48	3.633%	$239.8897	$239.89	$239.90	$239.90
7 purchase totals =	$995.41		$1,054.5618	$1,054.56	$1,054.55	$1,054.60