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	$78.71	13.705%	$89.4972	$89.50	$89.50	$89.50
Purchase #2	$160.31	4.194%	$167.0334	$167.03	$167.05	$167.00
Purchase #3	$166.83	12.174%	$187.1399	$187.14	$187.15	$187.10
Purchase #4	$128.58	6.563%	$137.0187	$137.02	$137.00	$137.00
Purchase #5	$28.89	13.507%	$32.7922	$32.79	$32.80	$32.80
Purchase #6	$20.96	6.311%	$22.2828	$22.28	$22.30	$22.30
Purchase #7	$63.33	7.693%	$68.202	$68.20	$68.20	$68.20
7 purchase totals =	$647.61		$703.9662	$703.96	$704.00	$703.90