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	$203.86	12.768%	$229.8888	$229.89	$229.90	$229.90
Purchase #2	$114.61	4.856%	$120.1755	$120.18	$120.20	$120.20
Purchase #3	$56.73	8.134%	$61.3444	$61.34	$61.35	$61.30
Purchase #4	$116.93	3.405%	$120.9115	$120.91	$120.90	$120.90
Purchase #5	$207.77	5.735%	$219.6856	$219.69	$219.70	$219.70
Purchase #6	$80.46	6.329%	$85.5523	$85.55	$85.55	$85.60
Purchase #7	$36.78	5.629%	$38.8503	$38.85	$38.85	$38.90
7 purchase totals =	$817.14		$876.4084	$876.41	$876.45	$876.50