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	$146.63	3.782%	$152.1755	$152.18	$152.20	$152.20
Purchase #2	$226.36	12.548%	$254.7637	$254.76	$254.75	$254.80
Purchase #3	$216.68	7.700%	$233.3644	$233.36	$233.35	$233.40
Purchase #4	$37.76	6.675%	$40.2805	$40.28	$40.30	$40.30
Purchase #5	$10.60	7.403%	$11.3847	$11.38	$11.40	$11.40
Purchase #6	$136.59	3.760%	$141.7258	$141.73	$141.75	$141.70
Purchase #7	$225.81	13.480%	$256.2492	$256.25	$256.25	$256.20
7 purchase totals =	$1,000.43		$1,089.9438	$1,089.94	$1,090.00	$1,090.00