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	$79.54	7.444%	$85.461	$85.46	$85.45	$85.50
Purchase #2	$58.86	12.851%	$66.4241	$66.42	$66.40	$66.40
Purchase #3	$160.31	5.528%	$169.1719	$169.17	$169.15	$169.20
Purchase #4	$217.33	8.404%	$235.5944	$235.59	$235.60	$235.60
Purchase #5	$156.53	9.221%	$170.9636	$170.96	$170.95	$171.00
Purchase #6	$79.90	13.540%	$90.7185	$90.72	$90.70	$90.70
Purchase #7	$36.73	10.759%	$40.6818	$40.68	$40.70	$40.70
7 purchase totals =	$789.20		$859.0153	$859.00	$858.95	$859.10