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	$228.30	6.817%	$243.8632	$243.86	$243.85	$243.90
Purchase #2	$63.48	13.562%	$72.0892	$72.09	$72.10	$72.10
Purchase #3	$144.70	9.348%	$158.2266	$158.23	$158.25	$158.20
Purchase #4	$44.88	5.382%	$47.2954	$47.30	$47.30	$47.30
Purchase #5	$187.27	4.797%	$196.2533	$196.25	$196.25	$196.30
Purchase #6	$46.59	11.355%	$51.8803	$51.88	$51.90	$51.90
Purchase #7	$109.45	11.698%	$122.2535	$122.25	$122.25	$122.30
7 purchase totals =	$824.67		$891.8615	$891.86	$891.90	$892.00