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	$19.59	11.656%	$21.8734	$21.87	$21.85	$21.90
Purchase #2	$91.32	12.261%	$102.5167	$102.52	$102.50	$102.50
Purchase #3	$193.73	4.654%	$202.7462	$202.75	$202.75	$202.70
Purchase #4	$215.73	3.304%	$222.8577	$222.86	$222.85	$222.90
Purchase #5	$229.38	5.858%	$242.8171	$242.82	$242.80	$242.80
Purchase #6	$40.74	4.285%	$42.4857	$42.49	$42.50	$42.50
Purchase #7	$87.49	4.839%	$91.7236	$91.72	$91.70	$91.70
7 purchase totals =	$877.98		$927.0204	$927.03	$926.95	$927.00