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	$16.79	9.502%	$18.3854	$18.39	$18.40	$18.40
Purchase #2	$175.47	7.832%	$189.2128	$189.21	$189.20	$189.20
Purchase #3	$82.31	8.752%	$89.5138	$89.51	$89.50	$89.50
Purchase #4	$86.74	4.383%	$90.5418	$90.54	$90.55	$90.50
Purchase #5	$46.29	5.568%	$48.8674	$48.87	$48.85	$48.90
Purchase #6	$120.88	3.366%	$124.9488	$124.95	$124.95	$124.90
Purchase #7	$220.86	9.508%	$241.8594	$241.86	$241.85	$241.90
7 purchase totals =	$749.34		$803.3294	$803.33	$803.30	$803.30