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	$57.41	4.326%	$59.8936	$59.89	$59.90	$59.90
Purchase #2	$17.42	5.370%	$18.3555	$18.36	$18.35	$18.40
Purchase #3	$154.98	6.447%	$164.9716	$164.97	$164.95	$165.00
Purchase #4	$188.61	10.577%	$208.5593	$208.56	$208.55	$208.60
Purchase #5	$195.94	13.489%	$222.3703	$222.37	$222.35	$222.40
Purchase #6	$117.63	6.211%	$124.936	$124.94	$124.95	$124.90
Purchase #7	$118.78	11.320%	$132.2259	$132.23	$132.25	$132.20
7 purchase totals =	$850.77		$931.3122	$931.32	$931.30	$931.40