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	$5.65	8.770%	$6.1455	$6.15	$6.15	$6.10
Purchase #2	$20.64	4.193%	$21.5054	$21.51	$21.50	$21.50
Purchase #3	$82.86	8.201%	$89.6553	$89.66	$89.65	$89.70
Purchase #4	$217.89	12.792%	$245.7625	$245.76	$245.75	$245.80
Purchase #5	$213.61	6.387%	$227.2533	$227.25	$227.25	$227.30
Purchase #6	$200.36	11.358%	$223.1169	$223.12	$223.10	$223.10
Purchase #7	$112.54	11.595%	$125.589	$125.59	$125.60	$125.60
7 purchase totals =	$853.55		$939.0279	$939.04	$939.00	$939.10