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	$6.59	9.849%	$7.239	$7.24	$7.25	$7.20
Purchase #2	$207.41	8.355%	$224.7391	$224.74	$224.75	$224.70
Purchase #3	$16.37	7.116%	$17.5349	$17.53	$17.55	$17.50
Purchase #4	$89.31	9.197%	$97.5238	$97.52	$97.50	$97.50
Purchase #5	$54.77	8.727%	$59.5498	$59.55	$59.55	$59.50
Purchase #6	$40.38	4.497%	$42.1959	$42.20	$42.20	$42.20
Purchase #7	$69.95	11.694%	$78.13	$78.13	$78.15	$78.10
7 purchase totals =	$484.78		$526.9125	$526.91	$526.95	$526.70