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	$73.40	3.394%	$75.8912	$75.89	$75.90	$75.90
Purchase #2	$146.96	10.496%	$162.3849	$162.38	$162.40	$162.40
Purchase #3	$142.46	8.191%	$154.1289	$154.13	$154.15	$154.10
Purchase #4	$148.89	12.437%	$167.4074	$167.41	$167.40	$167.40
Purchase #5	$57.42	4.308%	$59.8937	$59.89	$59.90	$59.90
Purchase #6	$5.29	3.258%	$5.4623	$5.46	$5.45	$5.50
Purchase #7	$18.39	3.856%	$19.0991	$19.10	$19.10	$19.10
7 purchase totals =	$592.81		$644.2675	$644.26	$644.30	$644.30