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	$19.91	9.113%	$21.7244	$21.72	$21.70	$21.70
Purchase #2	$134.25	10.144%	$147.8683	$147.87	$147.85	$147.90
Purchase #3	$66.48	9.663%	$72.904	$72.90	$72.90	$72.90
Purchase #4	$102.55	9.140%	$111.9231	$111.92	$111.90	$111.90
Purchase #5	$135.43	9.830%	$148.7428	$148.74	$148.75	$148.70
Purchase #6	$192.33	7.742%	$207.2202	$207.22	$207.20	$207.20
Purchase #7	$136.33	10.580%	$150.7537	$150.75	$150.75	$150.80
7 purchase totals =	$787.28		$861.1365	$861.12	$861.05	$861.10