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	$102.56	7.149%	$109.892	$109.89	$109.90	$109.90
Purchase #2	$34.89	11.431%	$38.8783	$38.88	$38.90	$38.90
Purchase #3	$92.42	12.413%	$103.8921	$103.89	$103.90	$103.90
Purchase #4	$67.51	7.153%	$72.339	$72.34	$72.35	$72.30
Purchase #5	$200.26	4.110%	$208.4907	$208.49	$208.50	$208.50
Purchase #6	$226.88	9.873%	$249.2799	$249.28	$249.30	$249.30
Purchase #7	$56.40	7.331%	$60.5347	$60.53	$60.55	$60.50
7 purchase totals =	$780.92		$843.3067	$843.30	$843.40	$843.30