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	$34.56	10.459%	$38.1746	$38.17	$38.15	$38.20
Purchase #2	$16.70	12.753%	$18.8298	$18.83	$18.85	$18.80
Purchase #3	$244.45	11.746%	$273.1631	$273.16	$273.15	$273.20
Purchase #4	$47.81	13.720%	$54.3695	$54.37	$54.35	$54.40
Purchase #5	$174.84	7.777%	$188.4373	$188.44	$188.45	$188.40
Purchase #6	$171.78	10.842%	$190.4044	$190.40	$190.40	$190.40
Purchase #7	$87.49	9.145%	$95.491	$95.49	$95.50	$95.50
7 purchase totals =	$777.63		$858.8697	$858.86	$858.85	$858.90