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	$206.43	4.205%	$215.1104	$215.11	$215.10	$215.10
Purchase #2	$113.46	6.761%	$121.131	$121.13	$121.15	$121.10
Purchase #3	$154.79	3.744%	$160.5853	$160.59	$160.60	$160.60
Purchase #4	$43.91	9.610%	$48.1298	$48.13	$48.15	$48.10
Purchase #5	$52.87	13.275%	$59.8885	$59.89	$59.90	$59.90
Purchase #6	$142.72	12.370%	$160.3745	$160.37	$160.35	$160.40
Purchase #7	$45.78	13.319%	$51.8774	$51.88	$51.90	$51.90
7 purchase totals =	$759.96		$817.0969	$817.10	$817.15	$817.10