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	$26.87	7.108%	$28.7799	$28.78	$28.80	$28.80
Purchase #2	$100.46	8.200%	$108.6977	$108.70	$108.70	$108.70
Purchase #3	$53.63	10.692%	$59.3641	$59.36	$59.35	$59.40
Purchase #4	$161.69	13.152%	$182.9555	$182.96	$182.95	$183.00
Purchase #5	$103.35	8.851%	$112.4975	$112.50	$112.50	$112.50
Purchase #6	$102.41	9.800%	$112.4462	$112.45	$112.45	$112.40
Purchase #7	$78.37	5.441%	$82.6341	$82.63	$82.65	$82.60
7 purchase totals =	$626.78		$687.3750	$687.38	$687.40	$687.40