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	$227.40	11.316%	$253.1326	$253.13	$253.15	$253.10
Purchase #2	$82.85	3.191%	$85.4937	$85.49	$85.50	$85.50
Purchase #3	$75.84	8.800%	$82.5139	$82.51	$82.50	$82.50
Purchase #4	$29.27	7.721%	$31.5299	$31.53	$31.55	$31.50
Purchase #5	$92.69	6.863%	$99.0513	$99.05	$99.05	$99.10
Purchase #6	$191.36	5.369%	$201.6341	$201.63	$201.65	$201.60
Purchase #7	$36.98	7.631%	$39.8019	$39.80	$39.80	$39.80
7 purchase totals =	$736.39		$793.1574	$793.14	$793.20	$793.10