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	$50.27	6.305%	$53.4395	$53.44	$53.45	$53.40
Purchase #2	$89.83	11.428%	$100.0958	$100.10	$100.10	$100.10
Purchase #3	$78.31	9.683%	$85.8928	$85.89	$85.90	$85.90
Purchase #4	$141.81	10.700%	$156.9837	$156.98	$157.00	$157.00
Purchase #5	$102.60	9.521%	$112.3685	$112.37	$112.35	$112.40
Purchase #6	$160.33	8.635%	$174.1745	$174.17	$174.15	$174.20
Purchase #7	$191.27	10.226%	$210.8293	$210.83	$210.85	$210.80
7 purchase totals =	$814.42		$893.7841	$893.78	$893.80	$893.80