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	$78.65	12.356%	$88.368	$88.37	$88.35	$88.40
Purchase #2	$228.93	10.676%	$253.3706	$253.37	$253.35	$253.40
Purchase #3	$145.72	13.106%	$164.8181	$164.82	$164.80	$164.80
Purchase #4	$222.88	9.115%	$243.1955	$243.20	$243.20	$243.20
Purchase #5	$101.80	3.687%	$105.5534	$105.55	$105.55	$105.60
Purchase #6	$144.81	5.780%	$153.18	$153.18	$153.20	$153.20
Purchase #7	$40.75	5.733%	$43.0862	$43.09	$43.10	$43.10
7 purchase totals =	$963.54		$1,051.5718	$1,051.58	$1,051.55	$1,051.70