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	$65.78	8.103%	$71.1102	$71.11	$71.10	$71.10
Purchase #2	$58.93	10.747%	$65.2632	$65.26	$65.25	$65.30
Purchase #3	$225.82	3.588%	$233.9224	$233.92	$233.90	$233.90
Purchase #4	$13.61	9.665%	$14.9254	$14.93	$14.95	$14.90
Purchase #5	$114.35	12.594%	$128.7512	$128.75	$128.75	$128.80
Purchase #6	$104.59	3.410%	$108.1565	$108.16	$108.15	$108.20
Purchase #7	$175.55	11.745%	$196.1683	$196.17	$196.15	$196.20
7 purchase totals =	$758.63		$818.2972	$818.30	$818.25	$818.40