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	$181.34	6.274%	$192.7173	$192.72	$192.70	$192.70
Purchase #2	$92.50	7.173%	$99.135	$99.14	$99.15	$99.10
Purchase #3	$136.65	5.130%	$143.6601	$143.66	$143.65	$143.70
Purchase #4	$241.37	4.107%	$251.2831	$251.28	$251.30	$251.30
Purchase #5	$38.50	13.490%	$43.6937	$43.69	$43.70	$43.70
Purchase #6	$9.52	4.176%	$9.9176	$9.92	$9.90	$9.90
Purchase #7	$85.86	5.357%	$90.4595	$90.46	$90.45	$90.50
7 purchase totals =	$785.74		$830.8663	$830.87	$830.85	$830.90