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	$15.96	10.230%	$17.5927	$17.59	$17.60	$17.60
Purchase #2	$16.48	5.853%	$17.4446	$17.44	$17.45	$17.40
Purchase #3	$113.67	10.787%	$125.9316	$125.93	$125.95	$125.90
Purchase #4	$85.40	5.788%	$90.343	$90.34	$90.35	$90.30
Purchase #5	$183.63	3.232%	$189.5649	$189.56	$189.55	$189.60
Purchase #6	$90.80	9.521%	$99.4451	$99.45	$99.45	$99.40
Purchase #7	$51.61	11.538%	$57.5648	$57.56	$57.55	$57.60
7 purchase totals =	$557.55		$597.8867	$597.87	$597.90	$597.80