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	$37.45	6.146%	$39.7517	$39.75	$39.75	$39.80
Purchase #2	$241.94	11.343%	$269.3833	$269.38	$269.40	$269.40
Purchase #3	$179.72	13.448%	$203.8887	$203.89	$203.90	$203.90
Purchase #4	$239.90	6.837%	$256.302	$256.30	$256.30	$256.30
Purchase #5	$100.98	11.768%	$112.8633	$112.86	$112.85	$112.90
Purchase #6	$198.92	8.325%	$215.4801	$215.48	$215.50	$215.50
Purchase #7	$209.62	3.662%	$217.2963	$217.30	$217.30	$217.30
7 purchase totals =	$1,208.53		$1,314.9654	$1,314.96	$1,315.00	$1,315.10