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	$20.33	3.786%	$21.0997	$21.10	$21.10	$21.10
Purchase #2	$118.43	13.187%	$134.0474	$134.05	$134.05	$134.00
Purchase #3	$166.56	11.506%	$185.7244	$185.72	$185.70	$185.70
Purchase #4	$35.64	4.571%	$37.2691	$37.27	$37.25	$37.30
Purchase #5	$225.81	12.231%	$253.4288	$253.43	$253.45	$253.40
Purchase #6	$152.80	10.312%	$168.5567	$168.56	$168.55	$168.60
Purchase #7	$106.85	10.376%	$117.9368	$117.94	$117.95	$117.90
7 purchase totals =	$826.42		$918.0629	$918.07	$918.05	$918.00