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	$69.86	11.845%	$78.1349	$78.13	$78.15	$78.10
Purchase #2	$216.96	3.476%	$224.5015	$224.50	$224.50	$224.50
Purchase #3	$88.54	7.725%	$95.3797	$95.38	$95.40	$95.40
Purchase #4	$142.25	9.548%	$155.832	$155.83	$155.85	$155.80
Purchase #5	$96.76	9.271%	$105.7306	$105.73	$105.75	$105.70
Purchase #6	$37.51	4.371%	$39.1496	$39.15	$39.15	$39.10
Purchase #7	$163.31	4.708%	$170.9986	$171.00	$171.00	$171.00
7 purchase totals =	$815.19		$869.7269	$869.72	$869.80	$869.60