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	$63.42	12.207%	$71.1617	$71.16	$71.15	$71.20
Purchase #2	$144.58	11.264%	$160.8655	$160.87	$160.85	$160.90
Purchase #3	$88.80	10.250%	$97.902	$97.90	$97.90	$97.90
Purchase #4	$231.78	13.145%	$262.2475	$262.25	$262.25	$262.20
Purchase #5	$155.84	3.439%	$161.1993	$161.20	$161.20	$161.20
Purchase #6	$90.82	9.845%	$99.7612	$99.76	$99.75	$99.80
Purchase #7	$146.96	6.578%	$156.627	$156.63	$156.65	$156.60
7 purchase totals =	$922.20		$1,009.7642	$1,009.77	$1,009.75	$1,009.80