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	$244.39	13.725%	$277.9325	$277.93	$277.95	$277.90
Purchase #2	$112.72	3.695%	$116.885	$116.89	$116.90	$116.90
Purchase #3	$34.49	9.795%	$37.8683	$37.87	$37.85	$37.90
Purchase #4	$218.76	12.252%	$245.5625	$245.56	$245.55	$245.60
Purchase #5	$190.88	5.112%	$200.6378	$200.64	$200.65	$200.60
Purchase #6	$138.25	9.300%	$151.1073	$151.11	$151.10	$151.10
Purchase #7	$89.91	3.769%	$93.2987	$93.30	$93.30	$93.30
7 purchase totals =	$1,029.40		$1,123.2921	$1,123.30	$1,123.30	$1,123.30