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	$170.52	9.123%	$186.0765	$186.08	$186.10	$186.10
Purchase #2	$36.29	3.351%	$37.5061	$37.51	$37.50	$37.50
Purchase #3	$223.32	7.124%	$239.2293	$239.23	$239.25	$239.20
Purchase #4	$43.43	4.374%	$45.3296	$45.33	$45.35	$45.30
Purchase #5	$193.52	10.667%	$214.1628	$214.16	$214.15	$214.20
Purchase #6	$39.77	5.762%	$42.0615	$42.06	$42.05	$42.10
Purchase #7	$163.83	13.840%	$186.5041	$186.50	$186.50	$186.50
7 purchase totals =	$870.68		$950.8699	$950.87	$950.90	$950.90