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	$12.81	5.229%	$13.4798	$13.48	$13.50	$13.50
Purchase #2	$170.61	8.520%	$185.146	$185.15	$185.15	$185.10
Purchase #3	$136.59	3.746%	$141.7067	$141.71	$141.70	$141.70
Purchase #4	$195.59	10.588%	$216.2991	$216.30	$216.30	$216.30
Purchase #5	$198.28	6.749%	$211.6619	$211.66	$211.65	$211.70
Purchase #6	$194.53	5.779%	$205.7719	$205.77	$205.75	$205.80
Purchase #7	$133.41	9.794%	$146.4762	$146.48	$146.50	$146.50
7 purchase totals =	$1,041.82		$1,120.5416	$1,120.55	$1,120.55	$1,120.60