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	$84.40	7.678%	$90.8802	$90.88	$90.90	$90.90
Purchase #2	$49.75	3.369%	$51.4261	$51.43	$51.45	$51.40
Purchase #3	$10.82	12.671%	$12.191	$12.19	$12.20	$12.20
Purchase #4	$213.93	9.336%	$233.9025	$233.90	$233.90	$233.90
Purchase #5	$186.85	10.674%	$206.7944	$206.79	$206.80	$206.80
Purchase #6	$225.89	11.783%	$252.5066	$252.51	$252.50	$252.50
Purchase #7	$93.82	5.587%	$99.0617	$99.06	$99.05	$99.10
7 purchase totals =	$865.46		$946.7625	$946.76	$946.80	$946.80