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	$118.41	13.272%	$134.1254	$134.13	$134.15	$134.10
Purchase #2	$220.51	6.231%	$234.25	$234.25	$234.25	$234.30
Purchase #3	$140.42	11.190%	$156.133	$156.13	$156.15	$156.10
Purchase #4	$210.70	5.647%	$222.5982	$222.60	$222.60	$222.60
Purchase #5	$162.49	10.792%	$180.0259	$180.03	$180.05	$180.00
Purchase #6	$205.37	4.496%	$214.6034	$214.60	$214.60	$214.60
Purchase #7	$87.75	12.700%	$98.8943	$98.89	$98.90	$98.90
7 purchase totals =	$1,145.65		$1,240.6302	$1,240.63	$1,240.70	$1,240.60