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	$187.90	4.626%	$196.5923	$196.59	$196.60	$196.60
Purchase #2	$146.45	13.328%	$165.9689	$165.97	$165.95	$166.00
Purchase #3	$168.40	13.671%	$191.422	$191.42	$191.40	$191.40
Purchase #4	$91.47	10.432%	$101.0122	$101.01	$101.00	$101.00
Purchase #5	$115.92	6.357%	$123.289	$123.29	$123.30	$123.30
Purchase #6	$53.32	12.238%	$59.8453	$59.85	$59.85	$59.80
Purchase #7	$29.84	12.830%	$33.6685	$33.67	$33.65	$33.70
7 purchase totals =	$793.30		$871.7982	$871.80	$871.75	$871.80