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	$34.36	9.332%	$37.5665	$37.57	$37.55	$37.60
Purchase #2	$65.45	12.437%	$73.59	$73.59	$73.60	$73.60
Purchase #3	$176.70	12.521%	$198.8246	$198.82	$198.80	$198.80
Purchase #4	$35.83	6.255%	$38.0712	$38.07	$38.05	$38.10
Purchase #5	$142.45	3.551%	$147.5084	$147.51	$147.50	$147.50
Purchase #6	$177.71	7.727%	$191.4417	$191.44	$191.45	$191.40
Purchase #7	$115.69	13.773%	$131.624	$131.62	$131.60	$131.60
7 purchase totals =	$748.19		$818.6264	$818.62	$818.55	$818.60