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	$52.34	12.500%	$58.8825	$58.88	$58.90	$58.90
Purchase #2	$157.85	6.677%	$168.3896	$168.39	$168.40	$168.40
Purchase #3	$118.85	11.784%	$132.8553	$132.86	$132.85	$132.90
Purchase #4	$149.76	5.118%	$157.4247	$157.42	$157.40	$157.40
Purchase #5	$104.30	5.367%	$109.8978	$109.90	$109.90	$109.90
Purchase #6	$128.73	11.831%	$143.96	$143.96	$143.95	$144.00
Purchase #7	$231.74	6.697%	$247.2596	$247.26	$247.25	$247.30
7 purchase totals =	$943.57		$1,018.6695	$1,018.67	$1,018.65	$1,018.80