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	$25.30	8.818%	$27.531	$27.53	$27.55	$27.50
Purchase #2	$153.79	7.151%	$164.7875	$164.79	$164.80	$164.80
Purchase #3	$132.45	10.469%	$146.3162	$146.32	$146.30	$146.30
Purchase #4	$213.39	6.807%	$227.9155	$227.92	$227.90	$227.90
Purchase #5	$75.90	10.238%	$83.6706	$83.67	$83.65	$83.70
Purchase #6	$109.26	13.114%	$123.5884	$123.59	$123.60	$123.60
Purchase #7	$189.97	10.298%	$209.5331	$209.53	$209.55	$209.50
7 purchase totals =	$900.06		$983.3423	$983.35	$983.35	$983.30