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	$116.79	13.495%	$132.5508	$132.55	$132.55	$132.60
Purchase #2	$52.51	9.419%	$57.4559	$57.46	$57.45	$57.50
Purchase #3	$84.34	7.520%	$90.6824	$90.68	$90.70	$90.70
Purchase #4	$69.61	4.728%	$72.9012	$72.90	$72.90	$72.90
Purchase #5	$97.91	8.275%	$106.0121	$106.01	$106.00	$106.00
Purchase #6	$174.36	9.310%	$190.5929	$190.59	$190.60	$190.60
Purchase #7	$169.71	10.471%	$187.4803	$187.48	$187.50	$187.50
7 purchase totals =	$765.23		$837.6756	$837.67	$837.70	$837.80