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	$38.77	8.778%	$42.1732	$42.17	$42.15	$42.20
Purchase #2	$31.37	6.576%	$33.4329	$33.43	$33.45	$33.40
Purchase #3	$200.73	5.215%	$211.1981	$211.20	$211.20	$211.20
Purchase #4	$35.35	6.743%	$37.7337	$37.73	$37.75	$37.70
Purchase #5	$181.81	12.457%	$204.4581	$204.46	$204.45	$204.50
Purchase #6	$247.27	5.801%	$261.6141	$261.61	$261.60	$261.60
Purchase #7	$180.78	4.158%	$188.2968	$188.30	$188.30	$188.30
7 purchase totals =	$916.08		$978.9069	$978.90	$978.90	$978.90