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	$8.30	6.134%	$8.8091	$8.81	$8.80	$8.80
Purchase #2	$107.50	4.614%	$112.4601	$112.46	$112.45	$112.50
Purchase #3	$55.88	7.156%	$59.8788	$59.88	$59.90	$59.90
Purchase #4	$163.65	10.157%	$180.2719	$180.27	$180.25	$180.30
Purchase #5	$159.30	4.763%	$166.8875	$166.89	$166.90	$166.90
Purchase #6	$161.38	6.819%	$172.3845	$172.38	$172.40	$172.40
Purchase #7	$209.99	13.129%	$237.5596	$237.56	$237.55	$237.60
7 purchase totals =	$866.00		$938.2515	$938.25	$938.25	$938.40