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	$59.95	5.534%	$63.2676	$63.27	$63.25	$63.30
Purchase #2	$33.47	13.511%	$37.9921	$37.99	$38.00	$38.00
Purchase #3	$145.80	13.550%	$165.5559	$165.56	$165.55	$165.60
Purchase #4	$31.31	6.641%	$33.3893	$33.39	$33.40	$33.40
Purchase #5	$137.29	10.602%	$151.8455	$151.85	$151.85	$151.80
Purchase #6	$41.56	5.456%	$43.8275	$43.83	$43.85	$43.80
Purchase #7	$145.96	9.754%	$160.1969	$160.20	$160.20	$160.20
7 purchase totals =	$595.34		$656.0748	$656.09	$656.10	$656.10