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	$187.38	6.497%	$199.5541	$199.55	$199.55	$199.60
Purchase #2	$18.58	13.769%	$21.1383	$21.14	$21.15	$21.10
Purchase #3	$213.43	12.590%	$240.3008	$240.30	$240.30	$240.30
Purchase #4	$188.97	5.758%	$199.8509	$199.85	$199.85	$199.90
Purchase #5	$88.34	6.853%	$94.3939	$94.39	$94.40	$94.40
Purchase #6	$38.25	8.793%	$41.6133	$41.61	$41.60	$41.60
Purchase #7	$235.79	12.180%	$264.5092	$264.51	$264.50	$264.50
7 purchase totals =	$970.74		$1,061.3605	$1,061.35	$1,061.35	$1,061.40