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	$27.36	6.548%	$29.1515	$29.15	$29.15	$29.20
Purchase #2	$40.40	6.530%	$43.0381	$43.04	$43.05	$43.00
Purchase #3	$240.40	8.158%	$260.0118	$260.01	$260.00	$260.00
Purchase #4	$205.84	5.655%	$217.4803	$217.48	$217.50	$217.50
Purchase #5	$109.67	12.219%	$123.0706	$123.07	$123.05	$123.10
Purchase #6	$66.74	10.309%	$73.6202	$73.62	$73.60	$73.60
Purchase #7	$182.89	7.190%	$196.0398	$196.04	$196.05	$196.00
7 purchase totals =	$873.30		$942.4123	$942.41	$942.40	$942.40