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	$194.60	3.245%	$200.9148	$200.91	$200.90	$200.90
Purchase #2	$155.96	8.283%	$168.8782	$168.88	$168.90	$168.90
Purchase #3	$141.30	10.731%	$156.4629	$156.46	$156.45	$156.50
Purchase #4	$153.75	4.567%	$160.7718	$160.77	$160.75	$160.80
Purchase #5	$32.40	11.828%	$36.2323	$36.23	$36.25	$36.20
Purchase #6	$49.45	9.813%	$54.3025	$54.30	$54.30	$54.30
Purchase #7	$22.91	7.313%	$24.5854	$24.59	$24.60	$24.60
7 purchase totals =	$750.37		$802.1479	$802.14	$802.15	$802.20