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	$24.61	13.467%	$27.9242	$27.92	$27.90	$27.90
Purchase #2	$35.82	10.121%	$39.4453	$39.45	$39.45	$39.40
Purchase #3	$205.77	12.382%	$231.2484	$231.25	$231.25	$231.20
Purchase #4	$87.90	10.134%	$96.8078	$96.81	$96.80	$96.80
Purchase #5	$165.40	5.870%	$175.109	$175.11	$175.10	$175.10
Purchase #6	$63.45	12.704%	$71.5107	$71.51	$71.50	$71.50
Purchase #7	$66.54	7.437%	$71.4886	$71.49	$71.50	$71.50
7 purchase totals =	$649.49		$713.5340	$713.54	$713.50	$713.40