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	$39.25	3.246%	$40.5241	$40.52	$40.50	$40.50
Purchase #2	$59.90	10.155%	$65.9828	$65.98	$66.00	$66.00
Purchase #3	$33.73	10.470%	$37.2615	$37.26	$37.25	$37.30
Purchase #4	$249.38	5.874%	$264.0286	$264.03	$264.05	$264.00
Purchase #5	$118.81	10.558%	$131.354	$131.35	$131.35	$131.40
Purchase #6	$220.28	3.370%	$227.7034	$227.70	$227.70	$227.70
Purchase #7	$224.89	13.377%	$254.9735	$254.97	$254.95	$255.00
7 purchase totals =	$946.24		$1,021.8279	$1,021.81	$1,021.80	$1,021.90