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	$31.89	4.690%	$33.3856	$33.39	$33.40	$33.40
Purchase #2	$171.78	10.537%	$189.8805	$189.88	$189.90	$189.90
Purchase #3	$169.98	12.681%	$191.5352	$191.54	$191.55	$191.50
Purchase #4	$116.47	11.761%	$130.168	$130.17	$130.15	$130.20
Purchase #5	$75.45	3.744%	$78.2748	$78.27	$78.25	$78.30
Purchase #6	$227.65	4.612%	$238.1492	$238.15	$238.15	$238.10
Purchase #7	$114.74	10.335%	$126.5984	$126.60	$126.60	$126.60
7 purchase totals =	$907.96		$987.9917	$988.00	$988.00	$988.00