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	$7.55	10.172%	$8.318	$8.32	$8.30	$8.30
Purchase #2	$59.37	3.518%	$61.4586	$61.46	$61.45	$61.50
Purchase #3	$123.80	6.594%	$131.9634	$131.96	$131.95	$132.00
Purchase #4	$234.89	7.287%	$252.0064	$252.01	$252.00	$252.00
Purchase #5	$225.67	13.274%	$255.6254	$255.63	$255.65	$255.60
Purchase #6	$160.29	9.203%	$175.0415	$175.04	$175.05	$175.00
Purchase #7	$199.46	8.511%	$216.436	$216.44	$216.45	$216.40
7 purchase totals =	$1,011.03		$1,100.8493	$1,100.86	$1,100.85	$1,100.80