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	$37.45	13.112%	$42.3604	$42.36	$42.35	$42.40
Purchase #2	$171.58	8.343%	$185.8949	$185.89	$185.90	$185.90
Purchase #3	$179.93	6.103%	$190.9111	$190.91	$190.90	$190.90
Purchase #4	$73.60	4.871%	$77.1851	$77.19	$77.20	$77.20
Purchase #5	$99.29	6.352%	$105.5969	$105.60	$105.60	$105.60
Purchase #6	$221.88	3.171%	$228.9158	$228.92	$228.90	$228.90
Purchase #7	$65.58	4.420%	$68.4786	$68.48	$68.50	$68.50
7 purchase totals =	$849.31		$899.3428	$899.35	$899.35	$899.40