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	$26.97	5.268%	$28.3908	$28.39	$28.40	$28.40
Purchase #2	$171.92	11.605%	$191.8713	$191.87	$191.85	$191.90
Purchase #3	$134.53	13.211%	$152.3028	$152.30	$152.30	$152.30
Purchase #4	$166.92	3.552%	$172.849	$172.85	$172.85	$172.80
Purchase #5	$180.66	6.702%	$192.7678	$192.77	$192.75	$192.80
Purchase #6	$80.83	12.406%	$90.8578	$90.86	$90.85	$90.90
Purchase #7	$101.55	9.147%	$110.8388	$110.84	$110.85	$110.80
7 purchase totals =	$863.38		$939.8783	$939.88	$939.85	$939.90