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	$246.91	9.421%	$270.1714	$270.17	$270.15	$270.20
Purchase #2	$33.73	13.763%	$38.3723	$38.37	$38.35	$38.40
Purchase #3	$227.59	11.535%	$253.8425	$253.84	$253.85	$253.80
Purchase #4	$47.72	6.686%	$50.9106	$50.91	$50.90	$50.90
Purchase #5	$237.78	6.861%	$254.0941	$254.09	$254.10	$254.10
Purchase #6	$72.48	13.618%	$82.3503	$82.35	$82.35	$82.40
Purchase #7	$166.82	13.571%	$189.4591	$189.46	$189.45	$189.50
7 purchase totals =	$1,033.03		$1,139.2003	$1,139.19	$1,139.15	$1,139.30