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	$124.36	9.660%	$136.3732	$136.37	$136.35	$136.40
Purchase #2	$70.40	11.714%	$78.6467	$78.65	$78.65	$78.60
Purchase #3	$241.41	7.309%	$259.0547	$259.05	$259.05	$259.10
Purchase #4	$17.35	4.384%	$18.1106	$18.11	$18.10	$18.10
Purchase #5	$189.81	5.358%	$199.98	$199.98	$200.00	$200.00
Purchase #6	$7.91	7.189%	$8.4786	$8.48	$8.50	$8.50
Purchase #7	$33.33	13.192%	$37.7269	$37.73	$37.75	$37.70
7 purchase totals =	$684.57		$738.3707	$738.37	$738.40	$738.40