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	$84.75	4.769%	$88.7917	$88.79	$88.80	$88.80
Purchase #2	$248.36	10.455%	$274.326	$274.33	$274.35	$274.30
Purchase #3	$78.64	4.540%	$82.2103	$82.21	$82.20	$82.20
Purchase #4	$204.71	10.202%	$225.5945	$225.59	$225.60	$225.60
Purchase #5	$136.70	4.271%	$142.5385	$142.54	$142.55	$142.50
Purchase #6	$58.25	13.191%	$65.9338	$65.93	$65.95	$65.90
Purchase #7	$149.52	12.713%	$168.5285	$168.53	$168.55	$168.50
7 purchase totals =	$960.93		$1,047.9233	$1,047.92	$1,048.00	$1,047.80