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	$242.42	6.641%	$258.5191	$258.52	$258.50	$258.50
Purchase #2	$135.59	10.842%	$150.2907	$150.29	$150.30	$150.30
Purchase #3	$55.26	10.120%	$60.8523	$60.85	$60.85	$60.90
Purchase #4	$136.44	3.687%	$141.4705	$141.47	$141.45	$141.50
Purchase #5	$179.40	3.338%	$185.3884	$185.39	$185.40	$185.40
Purchase #6	$32.73	5.326%	$34.4732	$34.47	$34.45	$34.50
Purchase #7	$61.38	3.437%	$63.4896	$63.49	$63.50	$63.50
7 purchase totals =	$843.22		$894.4838	$894.48	$894.45	$894.60