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	$69.77	13.186%	$78.9699	$78.97	$78.95	$79.00
Purchase #2	$30.48	10.585%	$33.7063	$33.71	$33.70	$33.70
Purchase #3	$190.92	9.548%	$209.149	$209.15	$209.15	$209.10
Purchase #4	$130.66	10.500%	$144.3793	$144.38	$144.40	$144.40
Purchase #5	$185.51	13.529%	$210.6076	$210.61	$210.60	$210.60
Purchase #6	$68.47	11.763%	$76.5241	$76.52	$76.50	$76.50
Purchase #7	$168.60	6.446%	$179.468	$179.47	$179.45	$179.50
7 purchase totals =	$844.41		$932.8042	$932.81	$932.75	$932.80