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	$81.32	6.722%	$86.7863	$86.79	$86.80	$86.80
Purchase #2	$27.54	8.243%	$29.8101	$29.81	$29.80	$29.80
Purchase #3	$63.35	13.276%	$71.7603	$71.76	$71.75	$71.80
Purchase #4	$55.52	3.585%	$57.5104	$57.51	$57.50	$57.50
Purchase #5	$136.58	6.717%	$145.7541	$145.75	$145.75	$145.80
Purchase #6	$182.91	12.352%	$205.503	$205.50	$205.50	$205.50
Purchase #7	$42.56	5.822%	$45.0378	$45.04	$45.05	$45.00
7 purchase totals =	$589.78		$642.1620	$642.16	$642.15	$642.20