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	$229.51	8.586%	$249.2157	$249.22	$249.20	$249.20
Purchase #2	$44.39	11.398%	$49.4496	$49.45	$49.45	$49.40
Purchase #3	$83.73	10.152%	$92.2303	$92.23	$92.25	$92.20
Purchase #4	$59.65	3.774%	$61.9012	$61.90	$61.90	$61.90
Purchase #5	$66.47	9.190%	$72.5786	$72.58	$72.60	$72.60
Purchase #6	$170.25	10.494%	$188.116	$188.12	$188.10	$188.10
Purchase #7	$242.43	10.504%	$267.8948	$267.89	$267.90	$267.90
7 purchase totals =	$896.43		$981.3862	$981.39	$981.40	$981.30