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	$118.43	11.661%	$132.2401	$132.24	$132.25	$132.20
Purchase #2	$123.58	6.682%	$131.8376	$131.84	$131.85	$131.80
Purchase #3	$200.56	6.368%	$213.3317	$213.33	$213.35	$213.30
Purchase #4	$59.69	10.282%	$65.8273	$65.83	$65.85	$65.80
Purchase #5	$76.45	9.759%	$83.9108	$83.91	$83.90	$83.90
Purchase #6	$121.79	5.426%	$128.3983	$128.40	$128.40	$128.40
Purchase #7	$146.70	9.340%	$160.4018	$160.40	$160.40	$160.40
7 purchase totals =	$847.20		$915.9476	$915.95	$916.00	$915.80