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	$155.80	8.333%	$168.7828	$168.78	$168.80	$168.80
Purchase #2	$99.75	9.686%	$109.4118	$109.41	$109.40	$109.40
Purchase #3	$65.49	13.327%	$74.2179	$74.22	$74.20	$74.20
Purchase #4	$172.89	6.783%	$184.6171	$184.62	$184.60	$184.60
Purchase #5	$99.35	10.659%	$109.9397	$109.94	$109.95	$109.90
Purchase #6	$40.60	10.686%	$44.9385	$44.94	$44.95	$44.90
Purchase #7	$210.48	9.819%	$231.147	$231.15	$231.15	$231.10
7 purchase totals =	$844.36		$923.0548	$923.06	$923.05	$922.90