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	$81.89	8.763%	$89.066	$89.07	$89.05	$89.10
Purchase #2	$85.84	11.316%	$95.5537	$95.55	$95.55	$95.60
Purchase #3	$44.91	6.506%	$47.8318	$47.83	$47.85	$47.80
Purchase #4	$125.61	13.727%	$142.8525	$142.85	$142.85	$142.90
Purchase #5	$96.48	5.756%	$102.0334	$102.03	$102.05	$102.00
Purchase #6	$153.27	7.136%	$164.2073	$164.21	$164.20	$164.20
Purchase #7	$61.58	9.177%	$67.2312	$67.23	$67.25	$67.20
7 purchase totals =	$649.58		$708.7759	$708.77	$708.80	$708.80