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	$249.85	13.863%	$284.4867	$284.49	$284.50	$284.50
Purchase #2	$130.29	11.209%	$144.8942	$144.89	$144.90	$144.90
Purchase #3	$99.38	10.699%	$110.0127	$110.01	$110.00	$110.00
Purchase #4	$17.32	6.458%	$18.4385	$18.44	$18.45	$18.40
Purchase #5	$189.82	7.747%	$204.5254	$204.53	$204.55	$204.50
Purchase #6	$42.66	6.827%	$45.5724	$45.57	$45.55	$45.60
Purchase #7	$78.96	5.829%	$83.5626	$83.56	$83.55	$83.60
7 purchase totals =	$808.28		$891.4925	$891.49	$891.50	$891.50