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	$38.25	9.554%	$41.9044	$41.90	$41.90	$41.90
Purchase #2	$79.89	5.609%	$84.371	$84.37	$84.35	$84.40
Purchase #3	$117.81	11.725%	$131.6232	$131.62	$131.60	$131.60
Purchase #4	$162.49	11.708%	$181.5143	$181.51	$181.50	$181.50
Purchase #5	$181.30	5.148%	$190.6333	$190.63	$190.65	$190.60
Purchase #6	$152.62	9.330%	$166.8594	$166.86	$166.85	$166.90
Purchase #7	$118.88	7.363%	$127.6331	$127.63	$127.65	$127.60
7 purchase totals =	$851.24		$924.5387	$924.52	$924.50	$924.50