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	$5.67	3.790%	$5.8849	$5.88	$5.90	$5.90
Purchase #2	$239.46	11.307%	$266.5357	$266.54	$266.55	$266.50
Purchase #3	$220.31	13.615%	$250.3052	$250.31	$250.30	$250.30
Purchase #4	$244.80	6.459%	$260.6116	$260.61	$260.60	$260.60
Purchase #5	$55.65	5.726%	$58.8365	$58.84	$58.85	$58.80
Purchase #6	$129.31	11.229%	$143.8302	$143.83	$143.85	$143.80
Purchase #7	$91.59	3.727%	$95.0036	$95.00	$95.00	$95.00
7 purchase totals =	$986.79		$1,081.0077	$1,081.01	$1,081.05	$1,080.90