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	$11.71	10.798%	$12.9744	$12.97	$12.95	$13.00
Purchase #2	$176.72	8.591%	$191.902	$191.90	$191.90	$191.90
Purchase #3	$98.59	11.457%	$109.8855	$109.89	$109.90	$109.90
Purchase #4	$132.97	7.336%	$142.7247	$142.72	$142.70	$142.70
Purchase #5	$69.58	12.497%	$78.2754	$78.28	$78.30	$78.30
Purchase #6	$139.61	10.248%	$153.9172	$153.92	$153.90	$153.90
Purchase #7	$54.49	7.820%	$58.7511	$58.75	$58.75	$58.80
7 purchase totals =	$683.67		$748.4303	$748.43	$748.40	$748.50