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	$156.27	7.829%	$168.5044	$168.50	$168.50	$168.50
Purchase #2	$143.41	11.483%	$159.8778	$159.88	$159.90	$159.90
Purchase #3	$175.33	9.443%	$191.8864	$191.89	$191.90	$191.90
Purchase #4	$98.80	10.513%	$109.1868	$109.19	$109.20	$109.20
Purchase #5	$195.87	6.128%	$207.8729	$207.87	$207.85	$207.90
Purchase #6	$20.54	11.828%	$22.9695	$22.97	$22.95	$23.00
Purchase #7	$96.98	7.856%	$104.5987	$104.60	$104.60	$104.60
7 purchase totals =	$887.20		$964.8965	$964.90	$964.90	$965.00