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	$100.96	10.774%	$111.8374	$111.84	$111.85	$111.80
Purchase #2	$94.41	5.739%	$99.8282	$99.83	$99.85	$99.80
Purchase #3	$219.71	8.706%	$238.838	$238.84	$238.85	$238.80
Purchase #4	$100.43	9.315%	$109.7851	$109.79	$109.80	$109.80
Purchase #5	$106.31	12.121%	$119.1958	$119.20	$119.20	$119.20
Purchase #6	$66.53	3.121%	$68.6064	$68.61	$68.60	$68.60
Purchase #7	$238.77	10.600%	$264.0796	$264.08	$264.10	$264.10
7 purchase totals =	$927.12		$1,012.1705	$1,012.19	$1,012.25	$1,012.10