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	$127.92	8.599%	$138.9198	$138.92	$138.90	$138.90
Purchase #2	$196.55	10.338%	$216.8693	$216.87	$216.85	$216.90
Purchase #3	$133.37	13.640%	$151.5617	$151.56	$151.55	$151.60
Purchase #4	$159.34	3.870%	$165.5065	$165.51	$165.50	$165.50
Purchase #5	$229.29	5.614%	$242.1623	$242.16	$242.15	$242.20
Purchase #6	$134.97	6.808%	$144.1588	$144.16	$144.15	$144.20
Purchase #7	$76.74	6.675%	$81.8624	$81.86	$81.85	$81.90
7 purchase totals =	$1,058.18		$1,141.0408	$1,141.04	$1,140.95	$1,141.20