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	$46.35	11.692%	$51.7692	$51.77	$51.75	$51.80
Purchase #2	$64.44	11.559%	$71.8886	$71.89	$71.90	$71.90
Purchase #3	$44.30	3.575%	$45.8837	$45.88	$45.90	$45.90
Purchase #4	$119.88	9.264%	$130.9857	$130.99	$131.00	$131.00
Purchase #5	$231.72	12.410%	$260.4765	$260.48	$260.50	$260.50
Purchase #6	$75.29	9.558%	$82.4862	$82.49	$82.50	$82.50
Purchase #7	$157.89	6.354%	$167.9223	$167.92	$167.90	$167.90
7 purchase totals =	$739.87		$811.4122	$811.42	$811.45	$811.50