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	$72.73	7.634%	$78.2822	$78.28	$78.30	$78.30
Purchase #2	$113.36	11.239%	$126.1005	$126.10	$126.10	$126.10
Purchase #3	$35.36	6.142%	$37.5318	$37.53	$37.55	$37.50
Purchase #4	$83.82	12.497%	$94.295	$94.30	$94.30	$94.30
Purchase #5	$239.59	6.540%	$255.2592	$255.26	$255.25	$255.30
Purchase #6	$84.72	7.695%	$91.2392	$91.24	$91.25	$91.20
Purchase #7	$157.74	3.299%	$162.9438	$162.94	$162.95	$162.90
7 purchase totals =	$787.32		$845.6517	$845.65	$845.70	$845.60