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	$12.63	6.828%	$13.4924	$13.49	$13.50	$13.50
Purchase #2	$165.72	9.477%	$181.4253	$181.43	$181.45	$181.40
Purchase #3	$189.25	9.158%	$206.5815	$206.58	$206.60	$206.60
Purchase #4	$101.72	9.779%	$111.6672	$111.67	$111.65	$111.70
Purchase #5	$15.34	13.419%	$17.3985	$17.40	$17.40	$17.40
Purchase #6	$30.63	4.516%	$32.0133	$32.01	$32.00	$32.00
Purchase #7	$171.42	6.148%	$181.9589	$181.96	$181.95	$182.00
7 purchase totals =	$686.71		$744.5371	$744.54	$744.55	$744.60