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	$82.56	9.372%	$90.2975	$90.30	$90.30	$90.30
Purchase #2	$42.67	5.332%	$44.9452	$44.95	$44.95	$44.90
Purchase #3	$152.82	6.749%	$163.1338	$163.13	$163.15	$163.10
Purchase #4	$31.52	4.554%	$32.9554	$32.96	$32.95	$33.00
Purchase #5	$203.90	3.448%	$210.9305	$210.93	$210.95	$210.90
Purchase #6	$199.27	7.268%	$213.7529	$213.75	$213.75	$213.80
Purchase #7	$96.91	3.553%	$100.3532	$100.35	$100.35	$100.40
7 purchase totals =	$809.65		$856.3685	$856.37	$856.40	$856.40