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	$10.52	10.164%	$11.5893	$11.59	$11.60	$11.60
Purchase #2	$55.89	6.427%	$59.4821	$59.48	$59.50	$59.50
Purchase #3	$124.40	6.590%	$132.598	$132.60	$132.60	$132.60
Purchase #4	$124.34	3.485%	$128.6732	$128.67	$128.65	$128.70
Purchase #5	$10.81	6.148%	$11.4746	$11.47	$11.45	$11.50
Purchase #6	$202.31	3.826%	$210.0504	$210.05	$210.05	$210.10
Purchase #7	$38.53	9.676%	$42.2582	$42.26	$42.25	$42.30
7 purchase totals =	$566.80		$596.1258	$596.12	$596.10	$596.30