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	$117.66	13.815%	$133.9147	$133.91	$133.90	$133.90
Purchase #2	$40.87	11.370%	$45.5169	$45.52	$45.50	$45.50
Purchase #3	$168.86	10.509%	$186.6055	$186.61	$186.60	$186.60
Purchase #4	$206.62	8.644%	$224.4802	$224.48	$224.50	$224.50
Purchase #5	$175.98	7.756%	$189.629	$189.63	$189.65	$189.60
Purchase #6	$70.66	11.639%	$78.8841	$78.88	$78.90	$78.90
Purchase #7	$35.74	10.319%	$39.428	$39.43	$39.45	$39.40
7 purchase totals =	$816.39		$898.4584	$898.46	$898.50	$898.40