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	$95.25	13.578%	$108.183	$108.18	$108.20	$108.20
Purchase #2	$221.43	7.299%	$237.5922	$237.59	$237.60	$237.60
Purchase #3	$87.86	13.796%	$99.9812	$99.98	$100.00	$100.00
Purchase #4	$15.98	13.785%	$18.1828	$18.18	$18.20	$18.20
Purchase #5	$41.64	11.817%	$46.5606	$46.56	$46.55	$46.60
Purchase #6	$171.62	4.743%	$179.7599	$179.76	$179.75	$179.80
Purchase #7	$86.44	3.415%	$89.3919	$89.39	$89.40	$89.40
7 purchase totals =	$720.22		$779.6516	$779.64	$779.70	$779.80