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	$171.39	10.250%	$188.9575	$188.96	$188.95	$189.00
Purchase #2	$42.61	12.567%	$47.9648	$47.96	$47.95	$48.00
Purchase #3	$193.54	4.152%	$201.5758	$201.58	$201.60	$201.60
Purchase #4	$59.25	4.869%	$62.1349	$62.13	$62.15	$62.10
Purchase #5	$167.67	10.516%	$185.3022	$185.30	$185.30	$185.30
Purchase #6	$90.91	4.580%	$95.0737	$95.07	$95.05	$95.10
Purchase #7	$52.50	13.310%	$59.4878	$59.49	$59.50	$59.50
7 purchase totals =	$777.87		$840.4967	$840.49	$840.50	$840.60