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	$12.33	3.462%	$12.7569	$12.76	$12.75	$12.80
Purchase #2	$119.62	5.799%	$126.5568	$126.56	$126.55	$126.60
Purchase #3	$159.29	6.437%	$169.5435	$169.54	$169.55	$169.50
Purchase #4	$115.73	10.492%	$127.8724	$127.87	$127.85	$127.90
Purchase #5	$73.33	6.587%	$78.1602	$78.16	$78.15	$78.20
Purchase #6	$158.67	10.844%	$175.8762	$175.88	$175.90	$175.90
Purchase #7	$170.95	9.386%	$186.9954	$187.00	$187.00	$187.00
7 purchase totals =	$809.92		$877.7614	$877.77	$877.75	$877.90