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	$121.95	7.776%	$131.4328	$131.43	$131.45	$131.40
Purchase #2	$143.72	8.618%	$156.1058	$156.11	$156.10	$156.10
Purchase #3	$139.79	4.277%	$145.7688	$145.77	$145.75	$145.80
Purchase #4	$111.89	11.780%	$125.0706	$125.07	$125.05	$125.10
Purchase #5	$42.46	6.362%	$45.1613	$45.16	$45.15	$45.20
Purchase #6	$214.86	11.696%	$239.99	$239.99	$240.00	$240.00
Purchase #7	$35.93	5.396%	$37.8688	$37.87	$37.85	$37.90
7 purchase totals =	$810.60		$881.3981	$881.40	$881.35	$881.50