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	$152.25	7.850%	$164.2016	$164.20	$164.20	$164.20
Purchase #2	$99.53	7.446%	$106.941	$106.94	$106.95	$106.90
Purchase #3	$54.61	8.827%	$59.4304	$59.43	$59.45	$59.40
Purchase #4	$172.87	10.462%	$190.9557	$190.96	$190.95	$191.00
Purchase #5	$99.38	8.721%	$108.0469	$108.05	$108.05	$108.00
Purchase #6	$82.25	6.869%	$87.8998	$87.90	$87.90	$87.90
Purchase #7	$119.85	10.810%	$132.8058	$132.81	$132.80	$132.80
7 purchase totals =	$780.74		$850.2812	$850.29	$850.30	$850.20