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	$66.89	4.164%	$69.6753	$69.68	$69.70	$69.70
Purchase #2	$209.88	11.739%	$234.5178	$234.52	$234.50	$234.50
Purchase #3	$75.35	4.759%	$78.9359	$78.94	$78.95	$78.90
Purchase #4	$82.95	3.465%	$85.8242	$85.82	$85.80	$85.80
Purchase #5	$189.59	9.797%	$208.1641	$208.16	$208.15	$208.20
Purchase #6	$84.66	5.150%	$89.02	$89.02	$89.00	$89.00
Purchase #7	$89.28	10.646%	$98.7847	$98.78	$98.80	$98.80
7 purchase totals =	$798.60		$864.9220	$864.92	$864.90	$864.90