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	$182.33	5.118%	$191.6616	$191.66	$191.65	$191.70
Purchase #2	$207.73	12.637%	$233.9808	$233.98	$234.00	$234.00
Purchase #3	$57.60	6.523%	$61.3572	$61.36	$61.35	$61.40
Purchase #4	$6.59	6.403%	$7.012	$7.01	$7.00	$7.00
Purchase #5	$80.59	10.675%	$89.193	$89.19	$89.20	$89.20
Purchase #6	$57.62	9.188%	$62.9141	$62.91	$62.90	$62.90
Purchase #7	$30.30	9.140%	$33.0694	$33.07	$33.05	$33.10
7 purchase totals =	$622.76		$679.1881	$679.18	$679.15	$679.30