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	$29.46	12.577%	$33.1652	$33.17	$33.15	$33.20
Purchase #2	$216.74	13.161%	$245.2652	$245.27	$245.25	$245.30
Purchase #3	$181.30	6.428%	$192.954	$192.95	$192.95	$193.00
Purchase #4	$234.57	12.425%	$263.7153	$263.72	$263.70	$263.70
Purchase #5	$182.33	5.807%	$192.9179	$192.92	$192.90	$192.90
Purchase #6	$82.89	3.349%	$85.666	$85.67	$85.65	$85.70
Purchase #7	$139.54	13.578%	$158.4867	$158.49	$158.50	$158.50
7 purchase totals =	$1,066.83		$1,172.1703	$1,172.19	$1,172.10	$1,172.30