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	$77.71	3.695%	$80.5814	$80.58	$80.60	$80.60
Purchase #2	$143.82	7.394%	$154.4541	$154.45	$154.45	$154.50
Purchase #3	$157.82	10.211%	$173.935	$173.94	$173.95	$173.90
Purchase #4	$110.82	11.253%	$123.2906	$123.29	$123.30	$123.30
Purchase #5	$162.31	9.845%	$178.2894	$178.29	$178.30	$178.30
Purchase #6	$161.93	12.571%	$182.2862	$182.29	$182.30	$182.30
Purchase #7	$72.32	9.102%	$78.9026	$78.90	$78.90	$78.90
7 purchase totals =	$886.73		$971.7393	$971.74	$971.80	$971.80