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	$239.75	12.365%	$269.3951	$269.40	$269.40	$269.40
Purchase #2	$79.32	12.824%	$89.492	$89.49	$89.50	$89.50
Purchase #3	$125.25	4.560%	$130.9614	$130.96	$130.95	$131.00
Purchase #4	$52.25	7.493%	$56.1651	$56.17	$56.15	$56.20
Purchase #5	$67.34	13.546%	$76.4619	$76.46	$76.45	$76.50
Purchase #6	$38.39	11.239%	$42.7047	$42.70	$42.70	$42.70
Purchase #7	$106.29	10.635%	$117.5939	$117.59	$117.60	$117.60
7 purchase totals =	$708.59		$782.7741	$782.77	$782.75	$782.90