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	$80.98	5.462%	$85.4031	$85.40	$85.40	$85.40
Purchase #2	$180.95	10.670%	$200.2574	$200.26	$200.25	$200.30
Purchase #3	$167.98	12.420%	$188.8431	$188.84	$188.85	$188.80
Purchase #4	$116.93	9.383%	$127.9015	$127.90	$127.90	$127.90
Purchase #5	$13.85	10.557%	$15.3121	$15.31	$15.30	$15.30
Purchase #6	$77.34	10.398%	$85.3818	$85.38	$85.40	$85.40
Purchase #7	$27.65	12.546%	$31.119	$31.12	$31.10	$31.10
7 purchase totals =	$665.68		$734.2180	$734.21	$734.20	$734.20