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	$186.91	6.828%	$199.6722	$199.67	$199.65	$199.70
Purchase #2	$153.60	5.872%	$162.6194	$162.62	$162.60	$162.60
Purchase #3	$124.43	5.845%	$131.7029	$131.70	$131.70	$131.70
Purchase #4	$188.26	4.297%	$196.3495	$196.35	$196.35	$196.30
Purchase #5	$156.53	7.855%	$168.8254	$168.83	$168.85	$168.80
Purchase #6	$183.69	11.187%	$204.2394	$204.24	$204.25	$204.20
Purchase #7	$194.84	11.313%	$216.8822	$216.88	$216.90	$216.90
7 purchase totals =	$1,188.26		$1,280.2910	$1,280.29	$1,280.30	$1,280.20