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	$53.83	10.359%	$59.4062	$59.41	$59.40	$59.40
Purchase #2	$57.68	7.742%	$62.1456	$62.15	$62.15	$62.10
Purchase #3	$77.82	9.253%	$85.0207	$85.02	$85.00	$85.00
Purchase #4	$68.56	4.446%	$71.6082	$71.61	$71.60	$71.60
Purchase #5	$246.25	8.394%	$266.9202	$266.92	$266.90	$266.90
Purchase #6	$244.50	7.209%	$262.126	$262.13	$262.15	$262.10
Purchase #7	$78.34	7.151%	$83.9421	$83.94	$83.95	$83.90
7 purchase totals =	$826.98		$891.1690	$891.18	$891.15	$891.00