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	$42.60	11.454%	$47.4794	$47.48	$47.50	$47.50
Purchase #2	$183.57	4.811%	$192.4016	$192.40	$192.40	$192.40
Purchase #3	$133.95	12.238%	$150.3428	$150.34	$150.35	$150.30
Purchase #4	$153.64	3.538%	$159.0758	$159.08	$159.10	$159.10
Purchase #5	$57.59	11.470%	$64.1956	$64.20	$64.20	$64.20
Purchase #6	$179.54	3.312%	$185.4864	$185.49	$185.50	$185.50
Purchase #7	$146.70	13.762%	$166.8889	$166.89	$166.90	$166.90
7 purchase totals =	$897.59		$965.8705	$965.88	$965.95	$965.90