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	$28.96	13.657%	$32.9151	$32.92	$32.90	$32.90
Purchase #2	$166.97	8.792%	$181.65	$181.65	$181.65	$181.70
Purchase #3	$186.80	5.108%	$196.3417	$196.34	$196.35	$196.30
Purchase #4	$161.49	3.665%	$167.4086	$167.41	$167.40	$167.40
Purchase #5	$135.76	9.622%	$148.8228	$148.82	$148.80	$148.80
Purchase #6	$247.63	6.827%	$264.5357	$264.54	$264.55	$264.50
Purchase #7	$112.78	4.693%	$118.0728	$118.07	$118.05	$118.10
7 purchase totals =	$1,040.39		$1,109.7467	$1,109.75	$1,109.70	$1,109.70