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	$39.88	6.483%	$42.4654	$42.47	$42.45	$42.50
Purchase #2	$151.73	8.606%	$164.7879	$164.79	$164.80	$164.80
Purchase #3	$164.35	5.601%	$173.5552	$173.56	$173.55	$173.60
Purchase #4	$232.57	11.573%	$259.4853	$259.49	$259.50	$259.50
Purchase #5	$244.80	12.284%	$274.8712	$274.87	$274.85	$274.90
Purchase #6	$90.80	12.811%	$102.4324	$102.43	$102.45	$102.40
Purchase #7	$238.90	4.837%	$250.4556	$250.46	$250.45	$250.50
7 purchase totals =	$1,163.03		$1,268.0530	$1,268.07	$1,268.05	$1,268.20