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	$131.68	12.224%	$147.7766	$147.78	$147.80	$147.80
Purchase #2	$90.60	7.356%	$97.2645	$97.26	$97.25	$97.30
Purchase #3	$190.25	10.466%	$210.1616	$210.16	$210.15	$210.20
Purchase #4	$52.91	7.464%	$56.8592	$56.86	$56.85	$56.90
Purchase #5	$72.88	7.642%	$78.4495	$78.45	$78.45	$78.40
Purchase #6	$127.39	3.219%	$131.4907	$131.49	$131.50	$131.50
Purchase #7	$231.27	10.511%	$255.5788	$255.58	$255.60	$255.60
7 purchase totals =	$896.98		$977.5809	$977.58	$977.60	$977.70