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	$9.43	10.171%	$10.3891	$10.39	$10.40	$10.40
Purchase #2	$217.35	4.614%	$227.3785	$227.38	$227.40	$227.40
Purchase #3	$109.61	12.870%	$123.7168	$123.72	$123.70	$123.70
Purchase #4	$71.86	10.562%	$79.4499	$79.45	$79.45	$79.40
Purchase #5	$185.35	3.808%	$192.4081	$192.41	$192.40	$192.40
Purchase #6	$196.26	7.143%	$210.2789	$210.28	$210.30	$210.30
Purchase #7	$156.36	3.116%	$161.2322	$161.23	$161.25	$161.20
7 purchase totals =	$946.22		$1,004.8535	$1,004.86	$1,004.90	$1,004.80