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	$190.96	9.623%	$209.3361	$209.34	$209.35	$209.30
Purchase #2	$54.96	8.848%	$59.8229	$59.82	$59.80	$59.80
Purchase #3	$63.66	11.533%	$71.0019	$71.00	$71.00	$71.00
Purchase #4	$54.68	4.666%	$57.2314	$57.23	$57.25	$57.20
Purchase #5	$49.74	7.451%	$53.4461	$53.45	$53.45	$53.40
Purchase #6	$129.82	7.645%	$139.7447	$139.74	$139.75	$139.70
Purchase #7	$80.75	11.479%	$90.0193	$90.02	$90.00	$90.00
7 purchase totals =	$624.57		$680.6024	$680.60	$680.60	$680.40