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	$42.39	7.460%	$45.5523	$45.55	$45.55	$45.60
Purchase #2	$111.86	7.188%	$119.9005	$119.90	$119.90	$119.90
Purchase #3	$67.82	12.500%	$76.2975	$76.30	$76.30	$76.30
Purchase #4	$17.42	6.815%	$18.6072	$18.61	$18.60	$18.60
Purchase #5	$141.37	3.651%	$146.5314	$146.53	$146.55	$146.50
Purchase #6	$119.68	9.698%	$131.2866	$131.29	$131.30	$131.30
Purchase #7	$57.33	12.558%	$64.5295	$64.53	$64.55	$64.50
7 purchase totals =	$557.87		$602.7050	$602.71	$602.75	$602.70