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	$18.94	13.642%	$21.5238	$21.52	$21.50	$21.50
Purchase #2	$114.64	5.526%	$120.975	$120.98	$121.00	$121.00
Purchase #3	$25.36	12.564%	$28.5462	$28.55	$28.55	$28.50
Purchase #4	$140.87	3.376%	$145.6258	$145.63	$145.65	$145.60
Purchase #5	$122.52	3.670%	$127.0165	$127.02	$127.00	$127.00
Purchase #6	$136.39	3.665%	$141.3887	$141.39	$141.40	$141.40
Purchase #7	$185.40	6.208%	$196.9096	$196.91	$196.90	$196.90
7 purchase totals =	$744.12		$781.9856	$782.00	$782.00	$781.90