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	$129.87	12.564%	$146.1869	$146.19	$146.20	$146.20
Purchase #2	$213.32	9.294%	$233.146	$233.15	$233.15	$233.10
Purchase #3	$78.72	10.371%	$86.8841	$86.88	$86.90	$86.90
Purchase #4	$225.38	12.826%	$254.2872	$254.29	$254.30	$254.30
Purchase #5	$241.54	12.269%	$271.1745	$271.17	$271.15	$271.20
Purchase #6	$104.36	13.673%	$118.6291	$118.63	$118.65	$118.60
Purchase #7	$148.54	5.240%	$156.3235	$156.32	$156.30	$156.30
7 purchase totals =	$1,141.73		$1,266.6313	$1,266.63	$1,266.65	$1,266.60