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	$78.96	5.441%	$83.2562	$83.26	$83.25	$83.30
Purchase #2	$25.63	5.340%	$26.9986	$27.00	$27.00	$27.00
Purchase #3	$163.38	13.560%	$185.5343	$185.53	$185.55	$185.50
Purchase #4	$168.83	12.765%	$190.3811	$190.38	$190.40	$190.40
Purchase #5	$208.39	13.624%	$236.7811	$236.78	$236.80	$236.80
Purchase #6	$119.89	10.354%	$132.3034	$132.30	$132.30	$132.30
Purchase #7	$247.41	3.310%	$255.5993	$255.60	$255.60	$255.60
7 purchase totals =	$1,012.49		$1,110.8540	$1,110.85	$1,110.90	$1,110.90