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	$28.94	7.604%	$31.1406	$31.14	$31.15	$31.10
Purchase #2	$180.56	8.744%	$196.3482	$196.35	$196.35	$196.30
Purchase #3	$39.74	11.452%	$44.291	$44.29	$44.30	$44.30
Purchase #4	$165.87	12.433%	$186.4926	$186.49	$186.50	$186.50
Purchase #5	$69.70	12.659%	$78.5233	$78.52	$78.50	$78.50
Purchase #6	$153.68	6.824%	$164.1671	$164.17	$164.15	$164.20
Purchase #7	$144.64	10.182%	$159.3672	$159.37	$159.35	$159.40
7 purchase totals =	$783.13		$860.3300	$860.33	$860.30	$860.30