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	$63.60	12.394%	$71.4826	$71.48	$71.50	$71.50
Purchase #2	$137.87	7.793%	$148.6142	$148.61	$148.60	$148.60
Purchase #3	$242.41	3.491%	$250.8725	$250.87	$250.85	$250.90
Purchase #4	$81.55	9.162%	$89.0216	$89.02	$89.00	$89.00
Purchase #5	$11.98	9.409%	$13.1072	$13.11	$13.10	$13.10
Purchase #6	$236.69	3.412%	$244.7659	$244.77	$244.75	$244.80
Purchase #7	$75.50	5.179%	$79.4101	$79.41	$79.40	$79.40
7 purchase totals =	$849.60		$897.2741	$897.27	$897.20	$897.30