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	$213.33	13.727%	$242.6138	$242.61	$242.60	$242.60
Purchase #2	$168.92	8.431%	$183.1616	$183.16	$183.15	$183.20
Purchase #3	$151.79	12.568%	$170.867	$170.87	$170.85	$170.90
Purchase #4	$137.53	3.191%	$141.9186	$141.92	$141.90	$141.90
Purchase #5	$92.26	7.348%	$99.0393	$99.04	$99.05	$99.00
Purchase #6	$22.85	11.591%	$25.4985	$25.50	$25.50	$25.50
Purchase #7	$40.52	4.660%	$42.4082	$42.41	$42.40	$42.40
7 purchase totals =	$827.20		$905.5070	$905.51	$905.45	$905.50