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	$67.96	13.828%	$77.3575	$77.36	$77.35	$77.40
Purchase #2	$219.59	6.729%	$234.3662	$234.37	$234.35	$234.40
Purchase #3	$32.89	4.634%	$34.4141	$34.41	$34.40	$34.40
Purchase #4	$82.42	10.342%	$90.9439	$90.94	$90.95	$90.90
Purchase #5	$124.79	4.496%	$130.4006	$130.40	$130.40	$130.40
Purchase #6	$206.57	4.436%	$215.7334	$215.73	$215.75	$215.70
Purchase #7	$129.78	7.650%	$139.7082	$139.71	$139.70	$139.70
7 purchase totals =	$864.00		$922.9239	$922.92	$922.90	$922.90