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	$31.54	4.310%	$32.8994	$32.90	$32.90	$32.90
Purchase #2	$120.68	11.459%	$134.5087	$134.51	$134.50	$134.50
Purchase #3	$118.72	7.586%	$127.7261	$127.73	$127.75	$127.70
Purchase #4	$205.48	8.479%	$222.9026	$222.90	$222.90	$222.90
Purchase #5	$234.40	12.694%	$264.1547	$264.15	$264.15	$264.20
Purchase #6	$67.64	6.676%	$72.1556	$72.16	$72.15	$72.20
Purchase #7	$62.65	6.732%	$66.8676	$66.87	$66.85	$66.90
7 purchase totals =	$841.11		$921.2147	$921.22	$921.20	$921.30