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	$118.56	4.227%	$123.5715	$123.57	$123.55	$123.60
Purchase #2	$229.53	4.584%	$240.0517	$240.05	$240.05	$240.10
Purchase #3	$78.83	13.166%	$89.2088	$89.21	$89.20	$89.20
Purchase #4	$132.99	8.562%	$144.3766	$144.38	$144.40	$144.40
Purchase #5	$83.89	8.276%	$90.8327	$90.83	$90.85	$90.80
Purchase #6	$25.85	11.451%	$28.8101	$28.81	$28.80	$28.80
Purchase #7	$192.83	12.666%	$217.2538	$217.25	$217.25	$217.30
7 purchase totals =	$862.48		$934.1052	$934.10	$934.10	$934.20