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	$105.54	12.645%	$118.8855	$118.89	$118.90	$118.90
Purchase #2	$244.65	7.127%	$262.0862	$262.09	$262.10	$262.10
Purchase #3	$130.25	13.787%	$148.2076	$148.21	$148.20	$148.20
Purchase #4	$145.72	7.608%	$156.8064	$156.81	$156.80	$156.80
Purchase #5	$52.40	5.429%	$55.2448	$55.24	$55.25	$55.20
Purchase #6	$81.92	8.365%	$88.7726	$88.77	$88.75	$88.80
Purchase #7	$69.39	13.716%	$78.9075	$78.91	$78.90	$78.90
7 purchase totals =	$829.87		$908.9106	$908.92	$908.90	$908.90