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	$71.63	9.651%	$78.543	$78.54	$78.55	$78.50
Purchase #2	$13.82	10.488%	$15.2694	$15.27	$15.25	$15.30
Purchase #3	$43.49	4.116%	$45.28	$45.28	$45.30	$45.30
Purchase #4	$44.37	7.351%	$47.6316	$47.63	$47.65	$47.60
Purchase #5	$48.72	4.473%	$50.8992	$50.90	$50.90	$50.90
Purchase #6	$238.72	4.674%	$249.8778	$249.88	$249.90	$249.90
Purchase #7	$145.69	9.850%	$160.0405	$160.04	$160.05	$160.00
7 purchase totals =	$606.44		$647.5415	$647.54	$647.60	$647.50