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	$16.49	10.639%	$18.2444	$18.24	$18.25	$18.20
Purchase #2	$147.81	13.421%	$167.6476	$167.65	$167.65	$167.60
Purchase #3	$98.34	11.203%	$109.357	$109.36	$109.35	$109.40
Purchase #4	$156.97	11.329%	$174.7531	$174.75	$174.75	$174.80
Purchase #5	$77.87	10.548%	$86.0837	$86.08	$86.10	$86.10
Purchase #6	$52.47	13.501%	$59.554	$59.55	$59.55	$59.60
Purchase #7	$50.81	6.463%	$54.0939	$54.09	$54.10	$54.10
7 purchase totals =	$600.76		$669.7337	$669.72	$669.75	$669.80