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	$248.39	12.449%	$279.3121	$279.31	$279.30	$279.30
Purchase #2	$80.42	8.294%	$87.09	$87.09	$87.10	$87.10
Purchase #3	$52.58	13.592%	$59.7267	$59.73	$59.75	$59.70
Purchase #4	$157.71	7.229%	$169.1109	$169.11	$169.10	$169.10
Purchase #5	$66.49	7.508%	$71.4821	$71.48	$71.50	$71.50
Purchase #6	$75.55	12.528%	$85.0149	$85.01	$85.00	$85.00
Purchase #7	$108.88	4.507%	$113.7872	$113.79	$113.80	$113.80
7 purchase totals =	$790.02		$865.5239	$865.52	$865.55	$865.50