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	$137.32	4.129%	$142.9899	$142.99	$143.00	$143.00
Purchase #2	$24.61	13.459%	$27.9223	$27.92	$27.90	$27.90
Purchase #3	$115.64	13.859%	$131.6665	$131.67	$131.65	$131.70
Purchase #4	$250.33	3.443%	$258.9489	$258.95	$258.95	$258.90
Purchase #5	$39.93	13.744%	$45.418	$45.42	$45.40	$45.40
Purchase #6	$130.34	6.854%	$139.2735	$139.27	$139.25	$139.30
Purchase #7	$156.33	8.442%	$169.5274	$169.53	$169.55	$169.50
7 purchase totals =	$854.50		$915.7465	$915.75	$915.70	$915.70