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	$86.89	3.773%	$90.1684	$90.17	$90.15	$90.20
Purchase #2	$98.91	4.444%	$103.3056	$103.31	$103.30	$103.30
Purchase #3	$31.45	13.657%	$35.7451	$35.75	$35.75	$35.70
Purchase #4	$203.83	13.411%	$231.1656	$231.17	$231.15	$231.20
Purchase #5	$170.26	8.314%	$184.4154	$184.42	$184.40	$184.40
Purchase #6	$215.86	8.846%	$234.955	$234.96	$234.95	$235.00
Purchase #7	$192.45	7.283%	$206.4661	$206.47	$206.45	$206.50
7 purchase totals =	$999.65		$1,086.2212	$1,086.25	$1,086.15	$1,086.30