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	$139.69	8.216%	$151.1669	$151.17	$151.15	$151.20
Purchase #2	$77.61	11.268%	$86.3551	$86.36	$86.35	$86.40
Purchase #3	$114.26	9.474%	$125.085	$125.09	$125.10	$125.10
Purchase #4	$179.34	7.598%	$192.9663	$192.97	$192.95	$193.00
Purchase #5	$33.39	13.280%	$37.8242	$37.82	$37.80	$37.80
Purchase #6	$74.48	4.762%	$78.0267	$78.03	$78.05	$78.00
Purchase #7	$107.31	10.250%	$118.3093	$118.31	$118.30	$118.30
7 purchase totals =	$726.08		$789.7335	$789.75	$789.70	$789.80