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	$109.84	12.341%	$123.3954	$123.40	$123.40	$123.40
Purchase #2	$134.98	9.238%	$147.4495	$147.45	$147.45	$147.40
Purchase #3	$119.39	8.592%	$129.648	$129.65	$129.65	$129.60
Purchase #4	$138.67	3.767%	$143.8937	$143.89	$143.90	$143.90
Purchase #5	$238.40	7.730%	$256.8283	$256.83	$256.85	$256.80
Purchase #6	$181.34	13.480%	$205.7846	$205.78	$205.80	$205.80
Purchase #7	$137.68	4.190%	$143.4488	$143.45	$143.45	$143.40
7 purchase totals =	$1,060.30		$1,150.4483	$1,150.45	$1,150.50	$1,150.30