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	$28.89	12.181%	$32.4091	$32.41	$32.40	$32.40
Purchase #2	$57.53	8.508%	$62.4247	$62.42	$62.40	$62.40
Purchase #3	$219.98	8.600%	$238.8983	$238.90	$238.90	$238.90
Purchase #4	$186.79	12.591%	$210.3087	$210.31	$210.30	$210.30
Purchase #5	$217.50	8.602%	$236.2094	$236.21	$236.20	$236.20
Purchase #6	$37.58	7.698%	$40.4729	$40.47	$40.45	$40.50
Purchase #7	$244.52	4.174%	$254.7263	$254.73	$254.75	$254.70
7 purchase totals =	$992.79		$1,075.4494	$1,075.45	$1,075.40	$1,075.40