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	$6.85	8.859%	$7.4568	$7.46	$7.45	$7.50
Purchase #2	$41.72	4.156%	$43.4539	$43.45	$43.45	$43.50
Purchase #3	$235.87	7.593%	$253.7796	$253.78	$253.80	$253.80
Purchase #4	$179.63	13.820%	$204.4549	$204.45	$204.45	$204.50
Purchase #5	$110.25	7.562%	$118.5871	$118.59	$118.60	$118.60
Purchase #6	$229.32	4.454%	$239.5339	$239.53	$239.55	$239.50
Purchase #7	$36.61	3.455%	$37.8749	$37.87	$37.85	$37.90
7 purchase totals =	$840.25		$905.1411	$905.13	$905.15	$905.30