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	$52.42	5.244%	$55.1689	$55.17	$55.15	$55.20
Purchase #2	$41.69	8.487%	$45.2282	$45.23	$45.25	$45.20
Purchase #3	$100.73	3.550%	$104.3059	$104.31	$104.30	$104.30
Purchase #4	$128.65	9.869%	$141.3465	$141.35	$141.35	$141.30
Purchase #5	$66.93	6.745%	$71.4444	$71.44	$71.45	$71.40
Purchase #6	$95.38	5.114%	$100.2577	$100.26	$100.25	$100.30
Purchase #7	$220.38	6.206%	$234.0568	$234.06	$234.05	$234.10
7 purchase totals =	$706.18		$751.8084	$751.82	$751.80	$751.80