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	$217.56	10.459%	$240.3146	$240.31	$240.30	$240.30
Purchase #2	$236.34	13.700%	$268.7186	$268.72	$268.70	$268.70
Purchase #3	$172.45	6.662%	$183.9386	$183.94	$183.95	$183.90
Purchase #4	$140.93	9.782%	$154.7158	$154.72	$154.70	$154.70
Purchase #5	$238.94	6.827%	$255.2524	$255.25	$255.25	$255.30
Purchase #6	$161.31	4.292%	$168.2334	$168.23	$168.25	$168.20
Purchase #7	$209.64	7.254%	$224.8473	$224.85	$224.85	$224.80
7 purchase totals =	$1,377.17		$1,496.0207	$1,496.02	$1,496.00	$1,495.90