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	$67.29	12.182%	$75.4873	$75.49	$75.50	$75.50
Purchase #2	$171.78	6.241%	$182.5008	$182.50	$182.50	$182.50
Purchase #3	$103.54	7.825%	$111.642	$111.64	$111.65	$111.60
Purchase #4	$30.57	7.838%	$32.9661	$32.97	$32.95	$33.00
Purchase #5	$165.66	12.173%	$185.8258	$185.83	$185.85	$185.80
Purchase #6	$111.47	9.147%	$121.6662	$121.67	$121.65	$121.70
Purchase #7	$91.79	13.808%	$104.4644	$104.46	$104.45	$104.50
7 purchase totals =	$742.10		$814.5526	$814.56	$814.55	$814.60