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	$71.81	8.752%	$78.0948	$78.09	$78.10	$78.10
Purchase #2	$218.45	13.429%	$247.7857	$247.79	$247.80	$247.80
Purchase #3	$45.56	11.698%	$50.8896	$50.89	$50.90	$50.90
Purchase #4	$11.45	8.732%	$12.4498	$12.45	$12.45	$12.40
Purchase #5	$76.66	12.307%	$86.0945	$86.09	$86.10	$86.10
Purchase #6	$43.50	8.591%	$47.2371	$47.24	$47.25	$47.20
Purchase #7	$133.74	10.343%	$147.5727	$147.57	$147.55	$147.60
7 purchase totals =	$601.17		$670.1242	$670.12	$670.15	$670.10