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	$179.97	11.457%	$200.5892	$200.59	$200.60	$200.60
Purchase #2	$162.78	10.485%	$179.8475	$179.85	$179.85	$179.80
Purchase #3	$83.83	6.126%	$88.9654	$88.97	$88.95	$89.00
Purchase #4	$156.69	7.383%	$168.2584	$168.26	$168.25	$168.30
Purchase #5	$153.97	4.495%	$160.891	$160.89	$160.90	$160.90
Purchase #6	$136.35	6.424%	$145.1091	$145.11	$145.10	$145.10
Purchase #7	$37.69	9.221%	$41.1654	$41.17	$41.15	$41.20
7 purchase totals =	$911.28		$984.8260	$984.84	$984.80	$984.90