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	$242.69	4.424%	$253.4266	$253.43	$253.45	$253.40
Purchase #2	$66.91	5.403%	$70.5251	$70.53	$70.55	$70.50
Purchase #3	$188.58	13.403%	$213.8554	$213.86	$213.85	$213.90
Purchase #4	$105.61	13.724%	$120.1039	$120.10	$120.10	$120.10
Purchase #5	$36.54	9.711%	$40.0884	$40.09	$40.10	$40.10
Purchase #6	$104.37	5.213%	$109.8108	$109.81	$109.80	$109.80
Purchase #7	$17.89	5.395%	$18.8552	$18.86	$18.85	$18.90
7 purchase totals =	$762.59		$826.6654	$826.68	$826.70	$826.70