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	$75.31	12.428%	$84.6695	$84.67	$84.65	$84.70
Purchase #2	$238.52	5.197%	$250.9159	$250.92	$250.90	$250.90
Purchase #3	$222.87	9.281%	$243.5546	$243.55	$243.55	$243.60
Purchase #4	$100.25	9.381%	$109.6545	$109.65	$109.65	$109.70
Purchase #5	$171.51	9.158%	$187.2169	$187.22	$187.20	$187.20
Purchase #6	$193.63	3.479%	$200.3664	$200.37	$200.35	$200.40
Purchase #7	$9.52	9.287%	$10.4041	$10.40	$10.40	$10.40
7 purchase totals =	$1,011.61		$1,086.7819	$1,086.78	$1,086.70	$1,086.90