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	$99.30	10.380%	$109.6073	$109.61	$109.60	$109.60
Purchase #2	$50.65	11.638%	$56.5446	$56.54	$56.55	$56.50
Purchase #3	$24.63	4.645%	$25.7741	$25.77	$25.75	$25.80
Purchase #4	$104.96	3.856%	$109.0073	$109.01	$109.00	$109.00
Purchase #5	$161.65	7.662%	$174.0356	$174.04	$174.05	$174.00
Purchase #6	$32.30	12.658%	$36.3885	$36.39	$36.40	$36.40
Purchase #7	$132.57	4.770%	$138.8936	$138.89	$138.90	$138.90
7 purchase totals =	$606.06		$650.2510	$650.25	$650.25	$650.20