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	$174.37	6.275%	$185.3117	$185.31	$185.30	$185.30
Purchase #2	$249.52	10.638%	$276.0639	$276.06	$276.05	$276.10
Purchase #3	$186.34	12.442%	$209.5244	$209.52	$209.50	$209.50
Purchase #4	$86.83	4.175%	$90.4552	$90.46	$90.45	$90.50
Purchase #5	$234.59	8.442%	$254.3941	$254.39	$254.40	$254.40
Purchase #6	$37.77	12.750%	$42.5857	$42.59	$42.60	$42.60
Purchase #7	$205.79	9.312%	$224.9532	$224.95	$224.95	$225.00
7 purchase totals =	$1,175.21		$1,283.2882	$1,283.28	$1,283.25	$1,283.40