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	$75.36	4.128%	$78.4709	$78.47	$78.45	$78.50
Purchase #2	$38.25	10.483%	$42.2597	$42.26	$42.25	$42.30
Purchase #3	$93.71	5.669%	$99.0224	$99.02	$99.00	$99.00
Purchase #4	$153.54	6.705%	$163.8349	$163.83	$163.85	$163.80
Purchase #5	$12.37	12.345%	$13.8971	$13.90	$13.90	$13.90
Purchase #6	$103.31	6.740%	$110.2731	$110.27	$110.25	$110.30
Purchase #7	$153.55	13.802%	$174.743	$174.74	$174.75	$174.70
7 purchase totals =	$630.09		$682.5011	$682.49	$682.45	$682.50