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	$82.33	13.278%	$93.2618	$93.26	$93.25	$93.30
Purchase #2	$128.68	6.712%	$137.317	$137.32	$137.30	$137.30
Purchase #3	$72.89	3.394%	$75.3639	$75.36	$75.35	$75.40
Purchase #4	$181.35	8.535%	$196.8282	$196.83	$196.85	$196.80
Purchase #5	$82.35	12.240%	$92.4296	$92.43	$92.45	$92.40
Purchase #6	$229.54	6.630%	$244.7585	$244.76	$244.75	$244.80
Purchase #7	$249.42	4.191%	$259.8732	$259.87	$259.85	$259.90
7 purchase totals =	$1,026.56		$1,099.8322	$1,099.83	$1,099.80	$1,099.90