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	$98.38	4.661%	$102.9655	$102.97	$102.95	$103.00
Purchase #2	$169.43	5.582%	$178.8876	$178.89	$178.90	$178.90
Purchase #3	$156.57	10.540%	$173.0725	$173.07	$173.05	$173.10
Purchase #4	$190.52	3.232%	$196.6776	$196.68	$196.70	$196.70
Purchase #5	$35.50	9.868%	$39.0031	$39.00	$39.00	$39.00
Purchase #6	$179.64	5.125%	$188.8466	$188.85	$188.85	$188.80
Purchase #7	$141.76	12.564%	$159.5707	$159.57	$159.55	$159.60
7 purchase totals =	$971.80		$1,039.0236	$1,039.03	$1,039.00	$1,039.10