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	$144.32	4.819%	$151.2748	$151.27	$151.25	$151.30
Purchase #2	$153.75	9.507%	$168.367	$168.37	$168.35	$168.40
Purchase #3	$147.25	4.844%	$154.3828	$154.38	$154.40	$154.40
Purchase #4	$154.32	3.154%	$159.1873	$159.19	$159.20	$159.20
Purchase #5	$132.71	13.684%	$150.87	$150.87	$150.85	$150.90
Purchase #6	$21.71	5.160%	$22.8302	$22.83	$22.85	$22.80
Purchase #7	$6.90	13.358%	$7.8217	$7.82	$7.80	$7.80
7 purchase totals =	$760.96		$814.7338	$814.73	$814.70	$814.80