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	$79.55	3.427%	$82.2762	$82.28	$82.30	$82.30
Purchase #2	$89.63	11.713%	$100.1284	$100.13	$100.15	$100.10
Purchase #3	$200.93	13.234%	$227.5211	$227.52	$227.50	$227.50
Purchase #4	$23.99	13.103%	$27.1334	$27.13	$27.15	$27.10
Purchase #5	$70.41	3.113%	$72.6019	$72.60	$72.60	$72.60
Purchase #6	$88.52	11.384%	$98.5971	$98.60	$98.60	$98.60
Purchase #7	$33.38	9.478%	$36.5438	$36.54	$36.55	$36.50
7 purchase totals =	$586.41		$644.8019	$644.80	$644.85	$644.70