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	$206.50	10.334%	$227.8397	$227.84	$227.85	$227.80
Purchase #2	$73.96	5.387%	$77.9442	$77.94	$77.95	$77.90
Purchase #3	$99.72	9.621%	$109.3141	$109.31	$109.30	$109.30
Purchase #4	$157.81	8.466%	$171.1702	$171.17	$171.15	$171.20
Purchase #5	$86.93	3.546%	$90.0125	$90.01	$90.00	$90.00
Purchase #6	$14.68	12.630%	$16.5341	$16.53	$16.55	$16.50
Purchase #7	$95.39	4.707%	$99.88	$99.88	$99.90	$99.90
7 purchase totals =	$734.99		$792.6948	$792.68	$792.70	$792.60