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	$118.91	3.810%	$123.4405	$123.44	$123.45	$123.40
Purchase #2	$38.98	7.299%	$41.8252	$41.83	$41.85	$41.80
Purchase #3	$229.81	11.710%	$256.7208	$256.72	$256.70	$256.70
Purchase #4	$113.39	12.528%	$127.5955	$127.60	$127.60	$127.60
Purchase #5	$130.31	7.537%	$140.1315	$140.13	$140.15	$140.10
Purchase #6	$191.62	9.522%	$209.8661	$209.87	$209.85	$209.90
Purchase #7	$10.98	3.600%	$11.3753	$11.38	$11.40	$11.40
7 purchase totals =	$834.00		$910.9549	$910.97	$911.00	$910.90