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	$171.35	13.136%	$193.8585	$193.86	$193.85	$193.90
Purchase #2	$227.39	13.653%	$258.4356	$258.44	$258.45	$258.40
Purchase #3	$18.71	9.266%	$20.4437	$20.44	$20.45	$20.40
Purchase #4	$196.84	13.429%	$223.2736	$223.27	$223.25	$223.30
Purchase #5	$166.59	13.443%	$188.9847	$188.98	$189.00	$189.00
Purchase #6	$84.67	10.779%	$93.7966	$93.80	$93.80	$93.80
Purchase #7	$108.94	3.275%	$112.5078	$112.51	$112.50	$112.50
7 purchase totals =	$974.49		$1,091.3005	$1,091.30	$1,091.30	$1,091.30