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	$173.94	4.170%	$181.1933	$181.19	$181.20	$181.20
Purchase #2	$50.61	10.196%	$55.7702	$55.77	$55.75	$55.80
Purchase #3	$118.85	10.321%	$131.1165	$131.12	$131.10	$131.10
Purchase #4	$52.67	13.590%	$59.8279	$59.83	$59.85	$59.80
Purchase #5	$232.76	10.225%	$256.5597	$256.56	$256.55	$256.60
Purchase #6	$38.78	8.844%	$42.2097	$42.21	$42.20	$42.20
Purchase #7	$119.59	3.677%	$123.9873	$123.99	$124.00	$124.00
7 purchase totals =	$787.20		$850.6646	$850.67	$850.65	$850.70