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	$123.55	3.384%	$127.7309	$127.73	$127.75	$127.70
Purchase #2	$160.96	8.115%	$174.0219	$174.02	$174.00	$174.00
Purchase #3	$77.90	5.746%	$82.3761	$82.38	$82.40	$82.40
Purchase #4	$42.27	6.505%	$45.0197	$45.02	$45.00	$45.00
Purchase #5	$105.71	4.771%	$110.7534	$110.75	$110.75	$110.80
Purchase #6	$224.99	4.196%	$234.4306	$234.43	$234.45	$234.40
Purchase #7	$113.88	5.131%	$119.7232	$119.72	$119.70	$119.70
7 purchase totals =	$849.26		$894.0558	$894.05	$894.05	$894.00