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	$199.37	12.272%	$223.8367	$223.84	$223.85	$223.80
Purchase #2	$168.59	10.169%	$185.7339	$185.73	$185.75	$185.70
Purchase #3	$73.93	11.775%	$82.6353	$82.64	$82.65	$82.60
Purchase #4	$12.89	13.662%	$14.651	$14.65	$14.65	$14.70
Purchase #5	$202.30	9.787%	$222.0991	$222.10	$222.10	$222.10
Purchase #6	$6.61	12.203%	$7.4166	$7.42	$7.40	$7.40
Purchase #7	$92.77	12.833%	$104.6752	$104.68	$104.70	$104.70
7 purchase totals =	$756.46		$841.0478	$841.06	$841.10	$841.00