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	$225.54	9.678%	$247.3678	$247.37	$247.35	$247.40
Purchase #2	$35.83	10.293%	$39.518	$39.52	$39.50	$39.50
Purchase #3	$55.34	10.800%	$61.3167	$61.32	$61.30	$61.30
Purchase #4	$90.26	10.754%	$99.9666	$99.97	$99.95	$100.00
Purchase #5	$171.96	6.743%	$183.5553	$183.56	$183.55	$183.60
Purchase #6	$81.51	7.263%	$87.4301	$87.43	$87.45	$87.40
Purchase #7	$52.94	9.228%	$57.8253	$57.83	$57.85	$57.80
7 purchase totals =	$713.38		$776.9798	$777.00	$776.95	$777.00