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	$120.26	11.420%	$133.9937	$133.99	$134.00	$134.00
Purchase #2	$91.78	8.506%	$99.5868	$99.59	$99.60	$99.60
Purchase #3	$89.50	7.735%	$96.4228	$96.42	$96.40	$96.40
Purchase #4	$202.59	10.548%	$223.9592	$223.96	$223.95	$224.00
Purchase #5	$155.78	9.427%	$170.4654	$170.47	$170.45	$170.50
Purchase #6	$116.39	12.156%	$130.5384	$130.54	$130.55	$130.50
Purchase #7	$88.88	3.339%	$91.8477	$91.85	$91.85	$91.80
7 purchase totals =	$865.18		$946.8140	$946.82	$946.80	$946.80