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	$53.42	6.492%	$56.888	$56.89	$56.90	$56.90
Purchase #2	$80.32	7.340%	$86.2155	$86.22	$86.20	$86.20
Purchase #3	$100.88	8.529%	$109.4841	$109.48	$109.50	$109.50
Purchase #4	$249.25	10.104%	$274.4342	$274.43	$274.45	$274.40
Purchase #5	$201.34	9.810%	$221.0915	$221.09	$221.10	$221.10
Purchase #6	$17.88	5.329%	$18.8328	$18.83	$18.85	$18.80
Purchase #7	$250.97	10.303%	$276.8274	$276.83	$276.85	$276.80
7 purchase totals =	$954.06		$1,043.7735	$1,043.77	$1,043.85	$1,043.70