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	$178.85	11.873%	$200.0849	$200.08	$200.10	$200.10
Purchase #2	$86.66	4.710%	$90.7417	$90.74	$90.75	$90.70
Purchase #3	$45.34	5.642%	$47.8981	$47.90	$47.90	$47.90
Purchase #4	$129.81	9.115%	$141.6422	$141.64	$141.65	$141.60
Purchase #5	$99.69	11.535%	$111.1892	$111.19	$111.20	$111.20
Purchase #6	$30.34	7.239%	$32.5363	$32.54	$32.55	$32.50
Purchase #7	$249.40	4.326%	$260.189	$260.19	$260.20	$260.20
7 purchase totals =	$820.09		$884.2814	$884.28	$884.35	$884.20