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	$5.79	13.585%	$6.5766	$6.58	$6.60	$6.60
Purchase #2	$36.83	10.118%	$40.5565	$40.56	$40.55	$40.60
Purchase #3	$211.75	10.834%	$234.691	$234.69	$234.70	$234.70
Purchase #4	$59.50	13.418%	$67.4837	$67.48	$67.50	$67.50
Purchase #5	$94.39	5.831%	$99.8939	$99.89	$99.90	$99.90
Purchase #6	$215.95	13.640%	$245.4056	$245.41	$245.40	$245.40
Purchase #7	$150.94	9.111%	$164.6921	$164.69	$164.70	$164.70
7 purchase totals =	$775.15		$859.2994	$859.30	$859.35	$859.40