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	$104.33	10.466%	$115.2492	$115.25	$115.25	$115.20
Purchase #2	$81.90	10.632%	$90.6076	$90.61	$90.60	$90.60
Purchase #3	$190.59	13.708%	$216.7161	$216.72	$216.70	$216.70
Purchase #4	$92.37	6.502%	$98.3759	$98.38	$98.40	$98.40
Purchase #5	$132.91	11.846%	$148.6545	$148.65	$148.65	$148.70
Purchase #6	$170.70	9.190%	$186.3873	$186.39	$186.40	$186.40
Purchase #7	$108.72	5.162%	$114.3321	$114.33	$114.35	$114.30
7 purchase totals =	$881.52		$970.3227	$970.33	$970.35	$970.30