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	$17.52	5.755%	$18.5283	$18.53	$18.55	$18.50
Purchase #2	$107.96	11.140%	$119.9867	$119.99	$120.00	$120.00
Purchase #3	$52.63	13.552%	$59.7624	$59.76	$59.75	$59.80
Purchase #4	$213.60	7.856%	$230.3804	$230.38	$230.40	$230.40
Purchase #5	$212.44	6.347%	$225.9236	$225.92	$225.90	$225.90
Purchase #6	$110.60	7.740%	$119.1604	$119.16	$119.15	$119.20
Purchase #7	$70.25	3.242%	$72.5275	$72.53	$72.55	$72.50
7 purchase totals =	$785.00		$846.2693	$846.27	$846.30	$846.30