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	$245.88	13.430%	$278.9017	$278.90	$278.90	$278.90
Purchase #2	$170.41	6.483%	$181.4577	$181.46	$181.45	$181.50
Purchase #3	$93.89	12.469%	$105.5971	$105.60	$105.60	$105.60
Purchase #4	$91.91	7.519%	$98.8207	$98.82	$98.80	$98.80
Purchase #5	$176.89	13.591%	$200.9311	$200.93	$200.95	$200.90
Purchase #6	$170.72	4.220%	$177.9244	$177.92	$177.90	$177.90
Purchase #7	$98.37	5.245%	$103.5295	$103.53	$103.55	$103.50
7 purchase totals =	$1,048.07		$1,147.1622	$1,147.16	$1,147.15	$1,147.10