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	$102.96	6.125%	$109.2663	$109.27	$109.25	$109.30
Purchase #2	$158.71	6.133%	$168.4437	$168.44	$168.45	$168.40
Purchase #3	$148.32	12.286%	$166.5426	$166.54	$166.55	$166.50
Purchase #4	$153.74	9.222%	$167.9179	$167.92	$167.90	$167.90
Purchase #5	$240.54	7.768%	$259.2251	$259.23	$259.25	$259.20
Purchase #6	$24.33	11.490%	$27.1255	$27.13	$27.15	$27.10
Purchase #7	$91.34	7.393%	$98.0928	$98.09	$98.10	$98.10
7 purchase totals =	$919.94		$996.6139	$996.62	$996.65	$996.50