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	$10.86	12.756%	$12.2453	$12.25	$12.25	$12.20
Purchase #2	$94.31	10.577%	$104.2852	$104.29	$104.30	$104.30
Purchase #3	$128.74	12.618%	$144.9844	$144.98	$145.00	$145.00
Purchase #4	$104.49	13.731%	$118.8375	$118.84	$118.85	$118.80
Purchase #5	$131.87	13.870%	$150.1604	$150.16	$150.15	$150.20
Purchase #6	$82.74	12.365%	$92.9708	$92.97	$92.95	$93.00
Purchase #7	$207.91	7.434%	$223.366	$223.37	$223.35	$223.40
7 purchase totals =	$760.92		$846.8496	$846.86	$846.85	$846.90