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	$231.27	8.234%	$250.3128	$250.31	$250.30	$250.30
Purchase #2	$127.46	3.246%	$131.5974	$131.60	$131.60	$131.60
Purchase #3	$72.45	3.191%	$74.7619	$74.76	$74.75	$74.80
Purchase #4	$117.54	12.178%	$131.854	$131.85	$131.85	$131.90
Purchase #5	$240.56	12.767%	$271.2723	$271.27	$271.25	$271.30
Purchase #6	$81.73	9.393%	$89.4069	$89.41	$89.40	$89.40
Purchase #7	$113.31	13.320%	$128.4029	$128.40	$128.40	$128.40
7 purchase totals =	$984.32		$1,077.6082	$1,077.60	$1,077.55	$1,077.70