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	$6.83	11.430%	$7.6107	$7.61	$7.60	$7.60
Purchase #2	$119.45	4.594%	$124.9375	$124.94	$124.95	$124.90
Purchase #3	$40.51	8.512%	$43.9582	$43.96	$43.95	$44.00
Purchase #4	$199.75	10.762%	$221.2471	$221.25	$221.25	$221.20
Purchase #5	$226.51	12.274%	$254.3118	$254.31	$254.30	$254.30
Purchase #6	$160.43	7.618%	$172.6516	$172.65	$172.65	$172.70
Purchase #7	$46.38	12.147%	$52.0138	$52.01	$52.00	$52.00
7 purchase totals =	$799.86		$876.7307	$876.73	$876.70	$876.70