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	$26.92	6.484%	$28.6655	$28.67	$28.65	$28.70
Purchase #2	$76.50	6.824%	$81.7204	$81.72	$81.70	$81.70
Purchase #3	$179.90	11.435%	$200.4716	$200.47	$200.45	$200.50
Purchase #4	$175.62	5.374%	$185.0578	$185.06	$185.05	$185.10
Purchase #5	$203.60	12.515%	$229.0805	$229.08	$229.10	$229.10
Purchase #6	$127.61	10.636%	$141.1826	$141.18	$141.20	$141.20
Purchase #7	$225.79	7.707%	$243.1916	$243.19	$243.20	$243.20
7 purchase totals =	$1,015.94		$1,109.3700	$1,109.37	$1,109.35	$1,109.50