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	$172.51	7.564%	$185.5587	$185.56	$185.55	$185.60
Purchase #2	$116.72	3.593%	$120.9137	$120.91	$120.90	$120.90
Purchase #3	$98.85	12.633%	$111.3377	$111.34	$111.35	$111.30
Purchase #4	$11.25	10.478%	$12.4288	$12.43	$12.45	$12.40
Purchase #5	$180.99	12.718%	$204.0083	$204.01	$204.00	$204.00
Purchase #6	$69.35	9.744%	$76.1075	$76.11	$76.10	$76.10
Purchase #7	$200.69	8.240%	$217.2269	$217.23	$217.25	$217.20
7 purchase totals =	$850.36		$927.5816	$927.59	$927.60	$927.50