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	$148.61	9.331%	$162.4768	$162.48	$162.50	$162.50
Purchase #2	$93.72	6.389%	$99.7078	$99.71	$99.70	$99.70
Purchase #3	$128.38	4.180%	$133.7463	$133.75	$133.75	$133.70
Purchase #4	$130.47	11.455%	$145.4153	$145.42	$145.40	$145.40
Purchase #5	$136.44	7.126%	$146.1627	$146.16	$146.15	$146.20
Purchase #6	$90.25	13.570%	$102.4969	$102.50	$102.50	$102.50
Purchase #7	$45.69	6.581%	$48.6969	$48.70	$48.70	$48.70
7 purchase totals =	$773.56		$838.7027	$838.72	$838.70	$838.70