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	$157.79	10.856%	$174.9197	$174.92	$174.90	$174.90
Purchase #2	$13.84	12.759%	$15.6058	$15.61	$15.60	$15.60
Purchase #3	$139.95	10.500%	$154.6448	$154.64	$154.65	$154.60
Purchase #4	$184.69	11.317%	$205.5914	$205.59	$205.60	$205.60
Purchase #5	$99.58	11.385%	$110.9172	$110.92	$110.90	$110.90
Purchase #6	$78.30	12.817%	$88.3357	$88.34	$88.35	$88.30
Purchase #7	$96.94	3.615%	$100.4444	$100.44	$100.45	$100.40
7 purchase totals =	$771.09		$850.4590	$850.46	$850.45	$850.30