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	$63.32	11.744%	$70.7563	$70.76	$70.75	$70.80
Purchase #2	$137.33	4.369%	$143.3299	$143.33	$143.35	$143.30
Purchase #3	$239.69	11.195%	$266.5233	$266.52	$266.50	$266.50
Purchase #4	$151.37	11.207%	$168.334	$168.33	$168.35	$168.30
Purchase #5	$111.48	13.372%	$126.3871	$126.39	$126.40	$126.40
Purchase #6	$60.47	12.673%	$68.1334	$68.13	$68.15	$68.10
Purchase #7	$65.25	4.113%	$67.9337	$67.93	$67.95	$67.90
7 purchase totals =	$828.91		$911.3977	$911.39	$911.45	$911.30