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	$129.56	11.439%	$144.3804	$144.38	$144.40	$144.40
Purchase #2	$118.98	13.693%	$135.2719	$135.27	$135.25	$135.30
Purchase #3	$136.86	10.848%	$151.7066	$151.71	$151.70	$151.70
Purchase #4	$38.55	10.575%	$42.6267	$42.63	$42.65	$42.60
Purchase #5	$24.32	12.390%	$27.3332	$27.33	$27.35	$27.30
Purchase #6	$110.77	4.167%	$115.3858	$115.39	$115.40	$115.40
Purchase #7	$82.27	10.822%	$91.1733	$91.17	$91.15	$91.20
7 purchase totals =	$641.31		$707.8779	$707.88	$707.90	$707.90