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	$133.83	9.746%	$146.8731	$146.87	$146.85	$146.90
Purchase #2	$136.64	4.353%	$142.5879	$142.59	$142.60	$142.60
Purchase #3	$29.41	3.102%	$30.3223	$30.32	$30.30	$30.30
Purchase #4	$167.61	11.751%	$187.3059	$187.31	$187.30	$187.30
Purchase #5	$108.69	7.295%	$116.6189	$116.62	$116.60	$116.60
Purchase #6	$91.73	7.491%	$98.6015	$98.60	$98.60	$98.60
Purchase #7	$197.48	9.828%	$216.8883	$216.89	$216.90	$216.90
7 purchase totals =	$865.39		$939.1979	$939.20	$939.15	$939.20