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	$82.83	9.755%	$90.9101	$90.91	$90.90	$90.90
Purchase #2	$70.59	4.463%	$73.7404	$73.74	$73.75	$73.70
Purchase #3	$22.94	11.715%	$25.6274	$25.63	$25.65	$25.60
Purchase #4	$232.42	5.249%	$244.6197	$244.62	$244.60	$244.60
Purchase #5	$31.56	9.285%	$34.4903	$34.49	$34.50	$34.50
Purchase #6	$165.59	3.638%	$171.6142	$171.61	$171.60	$171.60
Purchase #7	$103.52	12.644%	$116.6091	$116.61	$116.60	$116.60
7 purchase totals =	$709.45		$757.6112	$757.61	$757.60	$757.50