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	$29.79	13.579%	$33.8352	$33.84	$33.85	$33.80
Purchase #2	$198.32	8.759%	$215.6908	$215.69	$215.70	$215.70
Purchase #3	$209.65	3.541%	$217.0737	$217.07	$217.05	$217.10
Purchase #4	$244.96	12.709%	$276.092	$276.09	$276.10	$276.10
Purchase #5	$38.34	5.748%	$40.5438	$40.54	$40.55	$40.50
Purchase #6	$164.61	5.237%	$173.2306	$173.23	$173.25	$173.20
Purchase #7	$44.46	5.811%	$47.0436	$47.04	$47.05	$47.00
7 purchase totals =	$930.13		$1,003.5097	$1,003.50	$1,003.55	$1,003.40