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	$229.78	11.212%	$255.5429	$255.54	$255.55	$255.50
Purchase #2	$173.74	8.406%	$188.3446	$188.34	$188.35	$188.30
Purchase #3	$30.40	3.874%	$31.5777	$31.58	$31.60	$31.60
Purchase #4	$15.43	11.717%	$17.2379	$17.24	$17.25	$17.20
Purchase #5	$81.49	5.395%	$85.8864	$85.89	$85.90	$85.90
Purchase #6	$94.57	4.692%	$99.0072	$99.01	$99.00	$99.00
Purchase #7	$125.35	4.314%	$130.7576	$130.76	$130.75	$130.80
7 purchase totals =	$750.76		$808.3543	$808.36	$808.40	$808.30