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	$129.64	5.706%	$137.0373	$137.04	$137.05	$137.00
Purchase #2	$96.31	7.767%	$103.7904	$103.79	$103.80	$103.80
Purchase #3	$77.32	6.740%	$82.5314	$82.53	$82.55	$82.50
Purchase #4	$82.96	6.382%	$88.2545	$88.25	$88.25	$88.30
Purchase #5	$68.91	8.491%	$74.7611	$74.76	$74.75	$74.80
Purchase #6	$122.51	6.773%	$130.8076	$130.81	$130.80	$130.80
Purchase #7	$89.67	5.770%	$94.844	$94.84	$94.85	$94.80
7 purchase totals =	$667.32		$712.0263	$712.02	$712.05	$712.00