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	$126.78	3.308%	$130.9739	$130.97	$130.95	$131.00
Purchase #2	$69.77	12.373%	$78.4026	$78.40	$78.40	$78.40
Purchase #3	$248.36	12.444%	$279.2659	$279.27	$279.25	$279.30
Purchase #4	$74.78	6.827%	$79.8852	$79.89	$79.90	$79.90
Purchase #5	$15.27	8.118%	$16.5096	$16.51	$16.50	$16.50
Purchase #6	$25.61	7.404%	$27.5062	$27.51	$27.50	$27.50
Purchase #7	$218.75	7.191%	$234.4803	$234.48	$234.50	$234.50
7 purchase totals =	$779.32		$847.0237	$847.03	$847.00	$847.10