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	$18.87	9.623%	$20.6859	$20.69	$20.70	$20.70
Purchase #2	$164.81	13.533%	$187.1137	$187.11	$187.10	$187.10
Purchase #3	$39.41	3.491%	$40.7858	$40.79	$40.80	$40.80
Purchase #4	$99.31	9.717%	$108.96	$108.96	$108.95	$109.00
Purchase #5	$108.71	6.224%	$115.4761	$115.48	$115.50	$115.50
Purchase #6	$66.72	7.864%	$71.9669	$71.97	$71.95	$72.00
Purchase #7	$184.42	3.776%	$191.3837	$191.38	$191.40	$191.40
7 purchase totals =	$682.25		$736.3721	$736.38	$736.40	$736.50