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	$133.31	3.123%	$137.4733	$137.47	$137.45	$137.50
Purchase #2	$174.26	10.595%	$192.7228	$192.72	$192.70	$192.70
Purchase #3	$19.86	4.431%	$20.74	$20.74	$20.75	$20.70
Purchase #4	$90.29	10.234%	$99.5303	$99.53	$99.55	$99.50
Purchase #5	$27.78	12.500%	$31.2525	$31.25	$31.25	$31.30
Purchase #6	$191.86	12.558%	$215.9538	$215.95	$215.95	$216.00
Purchase #7	$95.28	11.454%	$106.1934	$106.19	$106.20	$106.20
7 purchase totals =	$732.64		$803.8661	$803.85	$803.85	$803.90