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	$220.88	13.423%	$250.5287	$250.53	$250.55	$250.50
Purchase #2	$26.34	4.167%	$27.4376	$27.44	$27.45	$27.40
Purchase #3	$97.43	3.562%	$100.9005	$100.90	$100.90	$100.90
Purchase #4	$46.91	3.278%	$48.4477	$48.45	$48.45	$48.40
Purchase #5	$52.72	5.157%	$55.4388	$55.44	$55.45	$55.40
Purchase #6	$139.49	3.587%	$144.4935	$144.49	$144.50	$144.50
Purchase #7	$91.32	5.419%	$96.2686	$96.27	$96.25	$96.30
7 purchase totals =	$675.09		$723.5154	$723.52	$723.55	$723.40