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	$99.81	10.149%	$109.9397	$109.94	$109.95	$109.90
Purchase #2	$50.49	13.462%	$57.287	$57.29	$57.30	$57.30
Purchase #3	$163.93	6.693%	$174.9018	$174.90	$174.90	$174.90
Purchase #4	$77.69	6.830%	$82.9962	$83.00	$83.00	$83.00
Purchase #5	$190.49	10.313%	$210.1352	$210.14	$210.15	$210.10
Purchase #6	$39.97	13.444%	$45.3436	$45.34	$45.35	$45.30
Purchase #7	$183.89	8.259%	$199.0775	$199.08	$199.10	$199.10
7 purchase totals =	$806.27		$879.6810	$879.69	$879.75	$879.60