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	$125.97	4.343%	$131.4409	$131.44	$131.45	$131.40
Purchase #2	$47.51	8.693%	$51.64	$51.64	$51.65	$51.60
Purchase #3	$196.29	13.478%	$222.746	$222.75	$222.75	$222.70
Purchase #4	$44.34	11.209%	$49.3101	$49.31	$49.30	$49.30
Purchase #5	$37.47	4.861%	$39.2914	$39.29	$39.30	$39.30
Purchase #6	$225.84	5.531%	$238.3312	$238.33	$238.35	$238.30
Purchase #7	$53.96	4.490%	$56.3828	$56.38	$56.40	$56.40
7 purchase totals =	$731.38		$789.1424	$789.14	$789.20	$789.00