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	$55.39	6.612%	$59.0524	$59.05	$59.05	$59.10
Purchase #2	$120.25	13.107%	$136.0112	$136.01	$136.00	$136.00
Purchase #3	$201.82	8.206%	$218.3813	$218.38	$218.40	$218.40
Purchase #4	$218.63	13.266%	$247.6335	$247.63	$247.65	$247.60
Purchase #5	$49.48	9.724%	$54.2914	$54.29	$54.30	$54.30
Purchase #6	$50.27	3.334%	$51.946	$51.95	$51.95	$51.90
Purchase #7	$77.94	9.392%	$85.2601	$85.26	$85.25	$85.30
7 purchase totals =	$773.78		$852.5759	$852.57	$852.60	$852.60