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	$54.37	11.732%	$60.7487	$60.75	$60.75	$60.70
Purchase #2	$36.44	7.418%	$39.1431	$39.14	$39.15	$39.10
Purchase #3	$113.90	8.773%	$123.8924	$123.89	$123.90	$123.90
Purchase #4	$178.70	3.156%	$184.3398	$184.34	$184.35	$184.30
Purchase #5	$49.31	4.256%	$51.4086	$51.41	$51.40	$51.40
Purchase #6	$164.41	11.743%	$183.7167	$183.72	$183.70	$183.70
Purchase #7	$116.89	9.592%	$128.1021	$128.10	$128.10	$128.10
7 purchase totals =	$714.02		$771.3514	$771.35	$771.35	$771.20