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	$39.41	8.604%	$42.8008	$42.80	$42.80	$42.80
Purchase #2	$168.89	12.631%	$190.2225	$190.22	$190.20	$190.20
Purchase #3	$57.67	9.757%	$63.2969	$63.30	$63.30	$63.30
Purchase #4	$28.45	13.335%	$32.2438	$32.24	$32.25	$32.20
Purchase #5	$78.72	5.505%	$83.0535	$83.05	$83.05	$83.10
Purchase #6	$162.62	12.799%	$183.4337	$183.43	$183.45	$183.40
Purchase #7	$107.74	11.319%	$119.9351	$119.94	$119.95	$119.90
7 purchase totals =	$643.50		$714.9863	$714.98	$715.00	$714.90