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	$58.64	9.772%	$64.3703	$64.37	$64.35	$64.40
Purchase #2	$59.76	12.699%	$67.3489	$67.35	$67.35	$67.30
Purchase #3	$212.67	4.160%	$221.5171	$221.52	$221.50	$221.50
Purchase #4	$151.75	3.595%	$157.2054	$157.21	$157.20	$157.20
Purchase #5	$215.47	10.745%	$238.6223	$238.62	$238.60	$238.60
Purchase #6	$229.45	3.695%	$237.9282	$237.93	$237.95	$237.90
Purchase #7	$135.47	12.859%	$152.8901	$152.89	$152.90	$152.90
7 purchase totals =	$1,063.21		$1,139.8823	$1,139.89	$1,139.85	$1,139.80