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	$35.29	5.273%	$37.1508	$37.15	$37.15	$37.20
Purchase #2	$147.33	13.850%	$167.7352	$167.74	$167.75	$167.70
Purchase #3	$87.31	3.659%	$90.5047	$90.50	$90.50	$90.50
Purchase #4	$242.70	7.333%	$260.4972	$260.50	$260.50	$260.50
Purchase #5	$171.71	5.336%	$180.8724	$180.87	$180.85	$180.90
Purchase #6	$113.38	9.287%	$123.9096	$123.91	$123.90	$123.90
Purchase #7	$6.53	13.800%	$7.4311	$7.43	$7.45	$7.40
7 purchase totals =	$804.25		$868.1010	$868.10	$868.10	$868.10