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	$81.81	5.485%	$86.2973	$86.30	$86.30	$86.30
Purchase #2	$114.87	10.797%	$127.2725	$127.27	$127.25	$127.30
Purchase #3	$94.89	4.733%	$99.3811	$99.38	$99.40	$99.40
Purchase #4	$98.44	13.163%	$111.3977	$111.40	$111.40	$111.40
Purchase #5	$80.77	5.546%	$85.2495	$85.25	$85.25	$85.20
Purchase #6	$26.76	4.642%	$28.0022	$28.00	$28.00	$28.00
Purchase #7	$122.46	9.656%	$134.2847	$134.28	$134.30	$134.30
7 purchase totals =	$620.00		$671.8850	$671.88	$671.90	$671.90