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	$85.93	4.789%	$90.0452	$90.05	$90.05	$90.00
Purchase #2	$51.43	11.324%	$57.2539	$57.25	$57.25	$57.30
Purchase #3	$175.76	11.612%	$196.1693	$196.17	$196.15	$196.20
Purchase #4	$193.45	5.128%	$203.3701	$203.37	$203.35	$203.40
Purchase #5	$125.28	12.858%	$141.3885	$141.39	$141.40	$141.40
Purchase #6	$77.70	3.602%	$80.4988	$80.50	$80.50	$80.50
Purchase #7	$139.51	3.424%	$144.2868	$144.29	$144.30	$144.30
7 purchase totals =	$849.06		$913.0126	$913.02	$913.00	$913.10