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	$25.51	6.110%	$27.0687	$27.07	$27.05	$27.10
Purchase #2	$66.54	9.647%	$72.9591	$72.96	$72.95	$73.00
Purchase #3	$212.30	10.147%	$233.8421	$233.84	$233.85	$233.80
Purchase #4	$162.59	13.311%	$184.2324	$184.23	$184.25	$184.20
Purchase #5	$95.96	4.861%	$100.6246	$100.62	$100.60	$100.60
Purchase #6	$28.85	7.569%	$31.0337	$31.03	$31.05	$31.00
Purchase #7	$58.98	3.724%	$61.1764	$61.18	$61.20	$61.20
7 purchase totals =	$650.73		$710.9370	$710.93	$710.95	$710.90