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	$153.93	13.600%	$174.8645	$174.86	$174.85	$174.90
Purchase #2	$91.56	5.700%	$96.7789	$96.78	$96.80	$96.80
Purchase #3	$134.74	10.297%	$148.6142	$148.61	$148.60	$148.60
Purchase #4	$10.38	4.527%	$10.8499	$10.85	$10.85	$10.80
Purchase #5	$137.70	9.360%	$150.5887	$150.59	$150.60	$150.60
Purchase #6	$197.74	11.466%	$220.4129	$220.41	$220.40	$220.40
Purchase #7	$164.81	10.716%	$182.471	$182.47	$182.45	$182.50
7 purchase totals =	$890.86		$984.5801	$984.57	$984.55	$984.60