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	$230.91	9.778%	$253.4884	$253.49	$253.50	$253.50
Purchase #2	$69.85	12.404%	$78.5142	$78.51	$78.50	$78.50
Purchase #3	$118.40	7.540%	$127.3274	$127.33	$127.35	$127.30
Purchase #4	$101.40	4.267%	$105.7267	$105.73	$105.75	$105.70
Purchase #5	$164.62	4.169%	$171.483	$171.48	$171.50	$171.50
Purchase #6	$202.51	9.151%	$221.0417	$221.04	$221.05	$221.00
Purchase #7	$82.60	12.792%	$93.1662	$93.17	$93.15	$93.20
7 purchase totals =	$970.29		$1,050.7476	$1,050.75	$1,050.80	$1,050.70