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	$186.89	13.758%	$212.6023	$212.60	$212.60	$212.60
Purchase #2	$67.82	13.665%	$77.0876	$77.09	$77.10	$77.10
Purchase #3	$137.94	8.705%	$149.9477	$149.95	$149.95	$149.90
Purchase #4	$127.84	4.682%	$133.8255	$133.83	$133.85	$133.80
Purchase #5	$19.48	6.717%	$20.7885	$20.79	$20.80	$20.80
Purchase #6	$224.89	11.263%	$250.2194	$250.22	$250.20	$250.20
Purchase #7	$232.57	10.154%	$256.1852	$256.19	$256.20	$256.20
7 purchase totals =	$997.43		$1,100.6562	$1,100.67	$1,100.70	$1,100.60