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	$176.62	12.763%	$199.162	$199.16	$199.15	$199.20
Purchase #2	$98.43	5.148%	$103.4972	$103.50	$103.50	$103.50
Purchase #3	$61.84	13.729%	$70.33	$70.33	$70.35	$70.30
Purchase #4	$210.96	12.550%	$237.4355	$237.44	$237.45	$237.40
Purchase #5	$52.89	8.731%	$57.5078	$57.51	$57.50	$57.50
Purchase #6	$43.48	5.417%	$45.8353	$45.84	$45.85	$45.80
Purchase #7	$96.28	7.209%	$103.2208	$103.22	$103.20	$103.20
7 purchase totals =	$740.50		$816.9886	$817.00	$817.00	$816.90