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	$134.27	5.817%	$142.0805	$142.08	$142.10	$142.10
Purchase #2	$151.88	3.322%	$156.9255	$156.93	$156.95	$156.90
Purchase #3	$134.78	11.464%	$150.2312	$150.23	$150.25	$150.20
Purchase #4	$195.72	7.210%	$209.8314	$209.83	$209.85	$209.80
Purchase #5	$180.88	5.628%	$191.0599	$191.06	$191.05	$191.10
Purchase #6	$209.77	10.531%	$231.8609	$231.86	$231.85	$231.90
Purchase #7	$245.84	10.671%	$272.0736	$272.07	$272.05	$272.10
7 purchase totals =	$1,253.14		$1,354.0630	$1,354.06	$1,354.10	$1,354.10