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	$90.80	10.705%	$100.5201	$100.52	$100.50	$100.50
Purchase #2	$39.35	3.395%	$40.6859	$40.69	$40.70	$40.70
Purchase #3	$36.37	4.308%	$37.9368	$37.94	$37.95	$37.90
Purchase #4	$109.74	7.653%	$118.1384	$118.14	$118.15	$118.10
Purchase #5	$24.48	7.300%	$26.267	$26.27	$26.25	$26.30
Purchase #6	$93.40	12.398%	$104.9797	$104.98	$105.00	$105.00
Purchase #7	$43.60	9.869%	$47.9029	$47.90	$47.90	$47.90
7 purchase totals =	$437.74		$476.4308	$476.44	$476.45	$476.40