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	$73.74	13.611%	$83.7768	$83.78	$83.80	$83.80
Purchase #2	$216.26	12.720%	$243.7683	$243.77	$243.75	$243.80
Purchase #3	$186.80	7.559%	$200.9202	$200.92	$200.90	$200.90
Purchase #4	$71.49	9.278%	$78.1228	$78.12	$78.10	$78.10
Purchase #5	$48.87	11.569%	$54.5238	$54.52	$54.50	$54.50
Purchase #6	$55.33	5.275%	$58.2487	$58.25	$58.25	$58.20
Purchase #7	$119.47	10.147%	$131.5926	$131.59	$131.60	$131.60
7 purchase totals =	$771.96		$850.9532	$850.95	$850.90	$850.90