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	$34.89	6.726%	$37.2367	$37.24	$37.25	$37.20
Purchase #2	$24.33	12.587%	$27.3924	$27.39	$27.40	$27.40
Purchase #3	$130.99	9.387%	$143.286	$143.29	$143.30	$143.30
Purchase #4	$234.40	13.347%	$265.6854	$265.69	$265.70	$265.70
Purchase #5	$107.87	5.571%	$113.8794	$113.88	$113.90	$113.90
Purchase #6	$85.41	4.744%	$89.4619	$89.46	$89.45	$89.50
Purchase #7	$41.92	3.492%	$43.3838	$43.38	$43.40	$43.40
7 purchase totals =	$659.81		$720.3256	$720.33	$720.40	$720.40