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	$43.52	13.790%	$49.5214	$49.52	$49.50	$49.50
Purchase #2	$182.53	4.141%	$190.0886	$190.09	$190.10	$190.10
Purchase #3	$210.61	5.753%	$222.7264	$222.73	$222.75	$222.70
Purchase #4	$86.60	10.655%	$95.8272	$95.83	$95.85	$95.80
Purchase #5	$12.47	12.222%	$13.9941	$13.99	$14.00	$14.00
Purchase #6	$89.93	3.269%	$92.8698	$92.87	$92.85	$92.90
Purchase #7	$155.95	10.522%	$172.3591	$172.36	$172.35	$172.40
7 purchase totals =	$781.61		$837.3866	$837.39	$837.40	$837.40